diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 3363987322a..ba92bd8d92b 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -4364,11 +4364,11 @@ namespace ts {
                         return getInferredType(context, i);
                     }
                 }
-                return t;
+                return t;
             };
             
             mapper.context = context;
-            return mapper;
+            return mapper;
         }
 
         function identityMapper(type: Type): Type {
@@ -10863,9 +10863,6 @@ namespace ts {
                 return;
             }
 
-            // Exports should be checked only if enclosing module contains both exported and non exported declarations.
-            // In case if all declarations are non-exported check is unnecessary.
-
             // if localSymbol is defined on node then node itself is exported - check is required
             let symbol = node.localSymbol;
             if (!symbol) {
@@ -10885,27 +10882,45 @@ namespace ts {
 
             // we use SymbolFlags.ExportValue, SymbolFlags.ExportType and SymbolFlags.ExportNamespace
             // to denote disjoint declarationSpaces (without making new enum type).
-            let exportedDeclarationSpaces: SymbolFlags = 0;
-            let nonExportedDeclarationSpaces: SymbolFlags = 0;
-            forEach(symbol.declarations, d => {
+            let exportedDeclarationSpaces = SymbolFlags.None;
+            let nonExportedDeclarationSpaces = SymbolFlags.None;
+            let defaultExportedDeclarationSpaces = SymbolFlags.None;
+            for (let d of symbol.declarations) {
                 let declarationSpaces = getDeclarationSpaces(d);
-                if (getEffectiveDeclarationFlags(d, NodeFlags.Export)) {
-                    exportedDeclarationSpaces |= declarationSpaces;
+                let effectiveDeclarationFlags = getEffectiveDeclarationFlags(d, NodeFlags.Export | NodeFlags.Default);
+
+                if (effectiveDeclarationFlags & NodeFlags.Export) {
+                    if (effectiveDeclarationFlags & NodeFlags.Default) {
+                        defaultExportedDeclarationSpaces |= declarationSpaces;
+                    }
+                    else {
+                        exportedDeclarationSpaces |= declarationSpaces;
+                    }
                 }
                 else {
                     nonExportedDeclarationSpaces |= declarationSpaces;
                 }
-            });
+            }
 
-            let commonDeclarationSpace = exportedDeclarationSpaces & nonExportedDeclarationSpaces;
+            // Spaces for anyting not declared a 'default export'.
+            let nonDefaultExportedDeclarationSpaces = exportedDeclarationSpaces | nonExportedDeclarationSpaces;
+            
+            let commonDeclarationSpacesForExportsAndLocals = exportedDeclarationSpaces & nonExportedDeclarationSpaces;
+            let commonDeclarationSpacesForDefaultAndNonDefault = defaultExportedDeclarationSpaces & nonDefaultExportedDeclarationSpaces;
 
-            if (commonDeclarationSpace) {
+            if (commonDeclarationSpacesForExportsAndLocals || commonDeclarationSpacesForDefaultAndNonDefault) {
                 // declaration spaces for exported and non-exported declarations intersect
-                forEach(symbol.declarations, d => {
-                    if (getDeclarationSpaces(d) & commonDeclarationSpace) {
+                for (let d of symbol.declarations) {
+                    let declarationSpaces = getDeclarationSpaces(d);
+                    
+                    // Only error on the declarations that conributed to the intersecting spaces.
+                    if (declarationSpaces & commonDeclarationSpacesForDefaultAndNonDefault) {
+                        error(d.name, Diagnostics.Merged_declaration_0_cannot_include_a_default_export_declaration_Consider_adding_a_separate_export_default_0_declaration_instead, declarationNameToString(d.name));
+                    }
+                    else if (declarationSpaces & commonDeclarationSpacesForExportsAndLocals) {
                         error(d.name, Diagnostics.Individual_declarations_in_merged_declaration_0_must_be_all_exported_or_all_local, declarationNameToString(d.name));
                     }
-                });
+                }
             }
 
             function getDeclarationSpaces(d: Declaration): SymbolFlags {
diff --git a/src/compiler/diagnosticInformationMap.generated.ts b/src/compiler/diagnosticInformationMap.generated.ts
index ecea3a76673..854d214fb74 100644
--- a/src/compiler/diagnosticInformationMap.generated.ts
+++ b/src/compiler/diagnosticInformationMap.generated.ts
@@ -294,7 +294,7 @@ namespace ts {
         Multiple_constructor_implementations_are_not_allowed: { code: 2392, category: DiagnosticCategory.Error, key: "Multiple constructor implementations are not allowed." },
         Duplicate_function_implementation: { code: 2393, category: DiagnosticCategory.Error, key: "Duplicate function implementation." },
         Overload_signature_is_not_compatible_with_function_implementation: { code: 2394, category: DiagnosticCategory.Error, key: "Overload signature is not compatible with function implementation." },
-        Individual_declarations_in_merged_declaration_0_must_be_all_exported_or_all_local: { code: 2395, category: DiagnosticCategory.Error, key: "Individual declarations in merged declaration {0} must be all exported or all local." },
+        Individual_declarations_in_merged_declaration_0_must_be_all_exported_or_all_local: { code: 2395, category: DiagnosticCategory.Error, key: "Individual declarations in merged declaration '{0}' must be all exported or all local." },
         Duplicate_identifier_arguments_Compiler_uses_arguments_to_initialize_rest_parameters: { code: 2396, category: DiagnosticCategory.Error, key: "Duplicate identifier 'arguments'. Compiler uses 'arguments' to initialize rest parameters." },
         Duplicate_identifier_this_Compiler_uses_variable_declaration_this_to_capture_this_reference: { code: 2399, category: DiagnosticCategory.Error, key: "Duplicate identifier '_this'. Compiler uses variable declaration '_this' to capture 'this' reference." },
         Expression_resolves_to_variable_declaration_this_that_compiler_uses_to_capture_this_reference: { code: 2400, category: DiagnosticCategory.Error, key: "Expression resolves to variable declaration '_this' that compiler uses to capture 'this' reference." },
@@ -425,6 +425,7 @@ namespace ts {
         JSX_element_class_does_not_support_attributes_because_it_does_not_have_a_0_property: { code: 2607, category: DiagnosticCategory.Error, key: "JSX element class does not support attributes because it does not have a '{0}' property" },
         The_global_type_JSX_0_may_not_have_more_than_one_property: { code: 2608, category: DiagnosticCategory.Error, key: "The global type 'JSX.{0}' may not have more than one property" },
         Cannot_emit_namespaced_JSX_elements_in_React: { code: 2650, category: DiagnosticCategory.Error, key: "Cannot emit namespaced JSX elements in React" },
+        Merged_declaration_0_cannot_include_a_default_export_declaration_Consider_adding_a_separate_export_default_0_declaration_instead: { code: 2651, category: DiagnosticCategory.Error, key: "Merged declaration '{0}' cannot include a default export declaration. Consider adding a separate 'export default {0}' declaration instead." },
         Import_declaration_0_is_using_private_name_1: { code: 4000, category: DiagnosticCategory.Error, key: "Import declaration '{0}' is using private name '{1}'." },
         Type_parameter_0_of_exported_class_has_or_is_using_private_name_1: { code: 4002, category: DiagnosticCategory.Error, key: "Type parameter '{0}' of exported class has or is using private name '{1}'." },
         Type_parameter_0_of_exported_interface_has_or_is_using_private_name_1: { code: 4004, category: DiagnosticCategory.Error, key: "Type parameter '{0}' of exported interface has or is using private name '{1}'." },
diff --git a/src/compiler/diagnosticMessages.json b/src/compiler/diagnosticMessages.json
index 2765d04f400..fd235a9d38a 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -1165,7 +1165,7 @@
         "category": "Error",
         "code": 2394
     },
-    "Individual declarations in merged declaration {0} must be all exported or all local.": {
+    "Individual declarations in merged declaration '{0}' must be all exported or all local.": {
         "category": "Error",
         "code": 2395
     },
@@ -1689,6 +1689,10 @@
         "category": "Error",
         "code": 2650
     },
+    "Merged declaration '{0}' cannot include a default export declaration. Consider adding a separate 'export default {0}' declaration instead.": {
+        "category": "Error",
+        "code": 2651
+    },
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
         "code": 4000
diff --git a/tests/baselines/reference/defaultExportsCannotMerge01.errors.txt b/tests/baselines/reference/defaultExportsCannotMerge01.errors.txt
new file mode 100644
index 00000000000..6e3955b4ef8
--- /dev/null
+++ b/tests/baselines/reference/defaultExportsCannotMerge01.errors.txt
@@ -0,0 +1,49 @@
+tests/cases/conformance/es6/modules/m1.ts(2,25): error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+tests/cases/conformance/es6/modules/m1.ts(11,18): error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+tests/cases/conformance/es6/modules/m2.ts(5,8): error TS2304: Cannot find name 'Entity'.
+tests/cases/conformance/es6/modules/m2.ts(6,8): error TS2503: Cannot find namespace 'Entity'.
+tests/cases/conformance/es6/modules/m2.ts(8,8): error TS2339: Property 'x' does not exist on type '() => number'.
+tests/cases/conformance/es6/modules/m2.ts(9,8): error TS2339: Property 'y' does not exist on type '() => number'.
+
+
+==== tests/cases/conformance/es6/modules/m1.ts (2 errors) ====
+    
+    export default function Decl() {
+                            ~~~~
+!!! error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+        return 0;
+    }
+    
+    export interface Decl {
+        p1: number;
+        p2: number;
+    }
+    
+    export namespace Decl {
+                     ~~~~
+!!! error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+        export var x = 10;
+        export var y = 20;
+    
+        interface I {
+        }
+    }
+    
+==== tests/cases/conformance/es6/modules/m2.ts (4 errors) ====
+    import Entity from "m1"
+    
+    Entity();
+    
+    var x: Entity;
+           ~~~~~~
+!!! error TS2304: Cannot find name 'Entity'.
+    var y: Entity.I;
+           ~~~~~~
+!!! error TS2503: Cannot find namespace 'Entity'.
+    
+    Entity.x;
+           ~
+!!! error TS2339: Property 'x' does not exist on type '() => number'.
+    Entity.y;
+           ~
+!!! error TS2339: Property 'y' does not exist on type '() => number'.
\ No newline at end of file
diff --git a/tests/baselines/reference/defaultExportsCannotMerge01.js b/tests/baselines/reference/defaultExportsCannotMerge01.js
new file mode 100644
index 00000000000..99b8ecab1d3
--- /dev/null
+++ b/tests/baselines/reference/defaultExportsCannotMerge01.js
@@ -0,0 +1,50 @@
+//// [tests/cases/conformance/es6/modules/defaultExportsCannotMerge01.ts] ////
+
+//// [m1.ts]
+
+export default function Decl() {
+    return 0;
+}
+
+export interface Decl {
+    p1: number;
+    p2: number;
+}
+
+export namespace Decl {
+    export var x = 10;
+    export var y = 20;
+
+    interface I {
+    }
+}
+
+//// [m2.ts]
+import Entity from "m1"
+
+Entity();
+
+var x: Entity;
+var y: Entity.I;
+
+Entity.x;
+Entity.y;
+
+//// [m1.js]
+function Decl() {
+    return 0;
+}
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = Decl;
+var Decl;
+(function (Decl) {
+    Decl.x = 10;
+    Decl.y = 20;
+})(Decl = exports.Decl || (exports.Decl = {}));
+//// [m2.js]
+var m1_1 = require("m1");
+m1_1.default();
+var x;
+var y;
+m1_1.default.x;
+m1_1.default.y;
diff --git a/tests/baselines/reference/defaultExportsCannotMerge02.errors.txt b/tests/baselines/reference/defaultExportsCannotMerge02.errors.txt
new file mode 100644
index 00000000000..ef4ecdccfc3
--- /dev/null
+++ b/tests/baselines/reference/defaultExportsCannotMerge02.errors.txt
@@ -0,0 +1,44 @@
+tests/cases/conformance/es6/modules/m1.ts(2,22): error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+tests/cases/conformance/es6/modules/m1.ts(5,18): error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+tests/cases/conformance/es6/modules/m2.ts(3,1): error TS2348: Value of type 'typeof Decl' is not callable. Did you mean to include 'new'?
+tests/cases/conformance/es6/modules/m2.ts(6,8): error TS2503: Cannot find namespace 'Entity'.
+tests/cases/conformance/es6/modules/m2.ts(8,13): error TS2339: Property 'p1' does not exist on type 'Decl'.
+tests/cases/conformance/es6/modules/m2.ts(8,20): error TS2339: Property 'p2' does not exist on type 'Decl'.
+
+
+==== tests/cases/conformance/es6/modules/m1.ts (2 errors) ====
+    
+    export default class Decl {
+                         ~~~~
+!!! error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+    }
+    
+    export interface Decl {
+                     ~~~~
+!!! error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+        p1: number;
+        p2: number;
+    }
+    
+    export namespace Decl {
+        interface I {
+        }
+    }
+    
+==== tests/cases/conformance/es6/modules/m2.ts (4 errors) ====
+    import Entity from "m1"
+    
+    Entity();
+    ~~~~~~~~
+!!! error TS2348: Value of type 'typeof Decl' is not callable. Did you mean to include 'new'?
+    
+    var x: Entity;
+    var y: Entity.I;
+           ~~~~~~
+!!! error TS2503: Cannot find namespace 'Entity'.
+    var z = new Entity();
+    var sum = z.p1 + z.p2
+                ~~
+!!! error TS2339: Property 'p1' does not exist on type 'Decl'.
+                       ~~
+!!! error TS2339: Property 'p2' does not exist on type 'Decl'.
\ No newline at end of file
diff --git a/tests/baselines/reference/defaultExportsCannotMerge02.js b/tests/baselines/reference/defaultExportsCannotMerge02.js
new file mode 100644
index 00000000000..e3897395c74
--- /dev/null
+++ b/tests/baselines/reference/defaultExportsCannotMerge02.js
@@ -0,0 +1,42 @@
+//// [tests/cases/conformance/es6/modules/defaultExportsCannotMerge02.ts] ////
+
+//// [m1.ts]
+
+export default class Decl {
+}
+
+export interface Decl {
+    p1: number;
+    p2: number;
+}
+
+export namespace Decl {
+    interface I {
+    }
+}
+
+//// [m2.ts]
+import Entity from "m1"
+
+Entity();
+
+var x: Entity;
+var y: Entity.I;
+var z = new Entity();
+var sum = z.p1 + z.p2
+
+//// [m1.js]
+var Decl = (function () {
+    function Decl() {
+    }
+    return Decl;
+})();
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = Decl;
+//// [m2.js]
+var m1_1 = require("m1");
+m1_1.default();
+var x;
+var y;
+var z = new m1_1.default();
+var sum = z.p1 + z.p2;
diff --git a/tests/baselines/reference/defaultExportsCannotMerge03.errors.txt b/tests/baselines/reference/defaultExportsCannotMerge03.errors.txt
new file mode 100644
index 00000000000..219b59a5633
--- /dev/null
+++ b/tests/baselines/reference/defaultExportsCannotMerge03.errors.txt
@@ -0,0 +1,47 @@
+tests/cases/conformance/es6/modules/m1.ts(2,22): error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+tests/cases/conformance/es6/modules/m1.ts(5,11): error TS2518: Only an ambient class can be merged with an interface.
+tests/cases/conformance/es6/modules/m1.ts(5,11): error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+tests/cases/conformance/es6/modules/m2.ts(3,1): error TS2348: Value of type 'typeof Decl' is not callable. Did you mean to include 'new'?
+tests/cases/conformance/es6/modules/m2.ts(6,8): error TS2503: Cannot find namespace 'Entity'.
+tests/cases/conformance/es6/modules/m2.ts(8,13): error TS2339: Property 'p1' does not exist on type 'Decl'.
+tests/cases/conformance/es6/modules/m2.ts(8,20): error TS2339: Property 'p2' does not exist on type 'Decl'.
+
+
+==== tests/cases/conformance/es6/modules/m1.ts (3 errors) ====
+    
+    export default class Decl {
+                         ~~~~
+!!! error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+    }
+    
+    interface Decl {
+              ~~~~
+!!! error TS2518: Only an ambient class can be merged with an interface.
+              ~~~~
+!!! error TS2651: Merged declaration 'Decl' cannot include a default export declaration. Consider adding a separate 'export default Decl' declaration instead.
+        p1: number;
+        p2: number;
+    }
+    
+    namespace Decl {
+        interface I {
+        }
+    }
+    
+==== tests/cases/conformance/es6/modules/m2.ts (4 errors) ====
+    import Entity from "m1"
+    
+    Entity();
+    ~~~~~~~~
+!!! error TS2348: Value of type 'typeof Decl' is not callable. Did you mean to include 'new'?
+    
+    var x: Entity;
+    var y: Entity.I;
+           ~~~~~~
+!!! error TS2503: Cannot find namespace 'Entity'.
+    var z = new Entity();
+    var sum = z.p1 + z.p2
+                ~~
+!!! error TS2339: Property 'p1' does not exist on type 'Decl'.
+                       ~~
+!!! error TS2339: Property 'p2' does not exist on type 'Decl'.
\ No newline at end of file
diff --git a/tests/baselines/reference/defaultExportsCannotMerge03.js b/tests/baselines/reference/defaultExportsCannotMerge03.js
new file mode 100644
index 00000000000..05e7de94120
--- /dev/null
+++ b/tests/baselines/reference/defaultExportsCannotMerge03.js
@@ -0,0 +1,42 @@
+//// [tests/cases/conformance/es6/modules/defaultExportsCannotMerge03.ts] ////
+
+//// [m1.ts]
+
+export default class Decl {
+}
+
+interface Decl {
+    p1: number;
+    p2: number;
+}
+
+namespace Decl {
+    interface I {
+    }
+}
+
+//// [m2.ts]
+import Entity from "m1"
+
+Entity();
+
+var x: Entity;
+var y: Entity.I;
+var z = new Entity();
+var sum = z.p1 + z.p2
+
+//// [m1.js]
+var Decl = (function () {
+    function Decl() {
+    }
+    return Decl;
+})();
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = Decl;
+//// [m2.js]
+var m1_1 = require("m1");
+m1_1.default();
+var x;
+var y;
+var z = new m1_1.default();
+var sum = z.p1 + z.p2;
diff --git a/tests/baselines/reference/defaultExportsCannotMerge04.errors.txt b/tests/baselines/reference/defaultExportsCannotMerge04.errors.txt
new file mode 100644
index 00000000000..ee36491e0c7
--- /dev/null
+++ b/tests/baselines/reference/defaultExportsCannotMerge04.errors.txt
@@ -0,0 +1,28 @@
+tests/cases/conformance/es6/modules/defaultExportsCannotMerge04.ts(2,25): error TS2651: Merged declaration 'Foo' cannot include a default export declaration. Consider adding a separate 'export default Foo' declaration instead.
+tests/cases/conformance/es6/modules/defaultExportsCannotMerge04.ts(5,11): error TS2651: Merged declaration 'Foo' cannot include a default export declaration. Consider adding a separate 'export default Foo' declaration instead.
+tests/cases/conformance/es6/modules/defaultExportsCannotMerge04.ts(9,11): error TS2395: Individual declarations in merged declaration 'Foo' must be all exported or all local.
+tests/cases/conformance/es6/modules/defaultExportsCannotMerge04.ts(12,18): error TS2395: Individual declarations in merged declaration 'Foo' must be all exported or all local.
+
+
+==== tests/cases/conformance/es6/modules/defaultExportsCannotMerge04.ts (4 errors) ====
+    
+    export default function Foo() {
+                            ~~~
+!!! error TS2651: Merged declaration 'Foo' cannot include a default export declaration. Consider adding a separate 'export default Foo' declaration instead.
+    }
+    
+    namespace Foo {
+              ~~~
+!!! error TS2651: Merged declaration 'Foo' cannot include a default export declaration. Consider adding a separate 'export default Foo' declaration instead.
+        export var x;
+    }
+    
+    interface Foo {
+              ~~~
+!!! error TS2395: Individual declarations in merged declaration 'Foo' must be all exported or all local.
+    }
+    
+    export interface Foo {
+                     ~~~
+!!! error TS2395: Individual declarations in merged declaration 'Foo' must be all exported or all local.
+    }
\ No newline at end of file
diff --git a/tests/baselines/reference/defaultExportsCannotMerge04.js b/tests/baselines/reference/defaultExportsCannotMerge04.js
new file mode 100644
index 00000000000..eb1122a8197
--- /dev/null
+++ b/tests/baselines/reference/defaultExportsCannotMerge04.js
@@ -0,0 +1,23 @@
+//// [defaultExportsCannotMerge04.ts]
+
+export default function Foo() {
+}
+
+namespace Foo {
+    export var x;
+}
+
+interface Foo {
+}
+
+export interface Foo {
+}
+
+//// [defaultExportsCannotMerge04.js]
+function Foo() {
+}
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = Foo;
+var Foo;
+(function (Foo) {
+})(Foo || (Foo = {}));
diff --git a/tests/baselines/reference/duplicateSymbolsExportMatching.errors.txt b/tests/baselines/reference/duplicateSymbolsExportMatching.errors.txt
index df4f8f13c31..85dd29b78a3 100644
--- a/tests/baselines/reference/duplicateSymbolsExportMatching.errors.txt
+++ b/tests/baselines/reference/duplicateSymbolsExportMatching.errors.txt
@@ -1,21 +1,21 @@
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(24,15): error TS2395: Individual declarations in merged declaration I must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(25,22): error TS2395: Individual declarations in merged declaration I must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(26,22): error TS2395: Individual declarations in merged declaration E must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(27,15): error TS2395: Individual declarations in merged declaration E must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(32,12): error TS2395: Individual declarations in merged declaration inst must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(35,19): error TS2395: Individual declarations in merged declaration inst must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(42,9): error TS2395: Individual declarations in merged declaration v must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(43,16): error TS2395: Individual declarations in merged declaration v must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(44,9): error TS2395: Individual declarations in merged declaration w must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(45,16): error TS2395: Individual declarations in merged declaration w must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(49,12): error TS2395: Individual declarations in merged declaration F must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(24,15): error TS2395: Individual declarations in merged declaration 'I' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(25,22): error TS2395: Individual declarations in merged declaration 'I' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(26,22): error TS2395: Individual declarations in merged declaration 'E' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(27,15): error TS2395: Individual declarations in merged declaration 'E' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(32,12): error TS2395: Individual declarations in merged declaration 'inst' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(35,19): error TS2395: Individual declarations in merged declaration 'inst' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(42,9): error TS2395: Individual declarations in merged declaration 'v' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(43,16): error TS2395: Individual declarations in merged declaration 'v' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(44,9): error TS2395: Individual declarations in merged declaration 'w' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(45,16): error TS2395: Individual declarations in merged declaration 'w' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(49,12): error TS2395: Individual declarations in merged declaration 'F' must be all exported or all local.
 tests/cases/compiler/duplicateSymbolsExportMatching.ts(49,12): error TS2434: A namespace declaration cannot be located prior to a class or function with which it is merged
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(52,21): error TS2395: Individual declarations in merged declaration F must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(56,11): error TS2395: Individual declarations in merged declaration C must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(57,12): error TS2395: Individual declarations in merged declaration C must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(58,19): error TS2395: Individual declarations in merged declaration C must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(64,11): error TS2395: Individual declarations in merged declaration D must be all exported or all local.
-tests/cases/compiler/duplicateSymbolsExportMatching.ts(65,18): error TS2395: Individual declarations in merged declaration D must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(52,21): error TS2395: Individual declarations in merged declaration 'F' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(56,11): error TS2395: Individual declarations in merged declaration 'C' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(57,12): error TS2395: Individual declarations in merged declaration 'C' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(58,19): error TS2395: Individual declarations in merged declaration 'C' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(64,11): error TS2395: Individual declarations in merged declaration 'D' must be all exported or all local.
+tests/cases/compiler/duplicateSymbolsExportMatching.ts(65,18): error TS2395: Individual declarations in merged declaration 'D' must be all exported or all local.
 
 
 ==== tests/cases/compiler/duplicateSymbolsExportMatching.ts (18 errors) ====
@@ -44,28 +44,28 @@ tests/cases/compiler/duplicateSymbolsExportMatching.ts(65,18): error TS2395: Ind
     module N2 {
         interface I { }
                   ~
-!!! error TS2395: Individual declarations in merged declaration I must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'I' must be all exported or all local.
         export interface I { } // error
                          ~
-!!! error TS2395: Individual declarations in merged declaration I must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'I' must be all exported or all local.
         export interface E { }
                          ~
-!!! error TS2395: Individual declarations in merged declaration E must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'E' must be all exported or all local.
         interface E { } // error
                   ~
-!!! error TS2395: Individual declarations in merged declaration E must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'E' must be all exported or all local.
     }
     
     // Should report error only once for instantiated module
     module M {
         module inst {
                ~~~~
-!!! error TS2395: Individual declarations in merged declaration inst must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'inst' must be all exported or all local.
             var t;
         }
         export module inst { // one error
                       ~~~~
-!!! error TS2395: Individual declarations in merged declaration inst must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'inst' must be all exported or all local.
             var t;
         }
     }
@@ -74,41 +74,41 @@ tests/cases/compiler/duplicateSymbolsExportMatching.ts(65,18): error TS2395: Ind
     module M2 {
         var v: string;
             ~
-!!! error TS2395: Individual declarations in merged declaration v must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'v' must be all exported or all local.
         export var v: string; // one error (visibility)
                    ~
-!!! error TS2395: Individual declarations in merged declaration v must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'v' must be all exported or all local.
         var w: number;
             ~
-!!! error TS2395: Individual declarations in merged declaration w must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'w' must be all exported or all local.
         export var w: string; // two errors (visibility and type mismatch)
                    ~
-!!! error TS2395: Individual declarations in merged declaration w must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'w' must be all exported or all local.
     }
     
     module M {
         module F {
                ~
-!!! error TS2395: Individual declarations in merged declaration F must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'F' must be all exported or all local.
                ~
 !!! error TS2434: A namespace declaration cannot be located prior to a class or function with which it is merged
             var t;
         }
         export function F() { } // Only one error for duplicate identifier (don't consider visibility)
                         ~
-!!! error TS2395: Individual declarations in merged declaration F must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'F' must be all exported or all local.
     }
     
     module M {
         class C { }
               ~
-!!! error TS2395: Individual declarations in merged declaration C must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'C' must be all exported or all local.
         module C { }
                ~
-!!! error TS2395: Individual declarations in merged declaration C must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'C' must be all exported or all local.
         export module C { // Two visibility errors (one for the clodule symbol, and one for the merged container symbol)
                       ~
-!!! error TS2395: Individual declarations in merged declaration C must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'C' must be all exported or all local.
             var t;
         }
     }
@@ -116,7 +116,7 @@ tests/cases/compiler/duplicateSymbolsExportMatching.ts(65,18): error TS2395: Ind
     // Top level
     interface D { }
               ~
-!!! error TS2395: Individual declarations in merged declaration D must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'D' must be all exported or all local.
     export interface D { }
                      ~
-!!! error TS2395: Individual declarations in merged declaration D must be all exported or all local.
\ No newline at end of file
+!!! error TS2395: Individual declarations in merged declaration 'D' must be all exported or all local.
\ No newline at end of file
diff --git a/tests/baselines/reference/innerModExport2.errors.txt b/tests/baselines/reference/innerModExport2.errors.txt
index 52a9d01c997..f9568bb45a4 100644
--- a/tests/baselines/reference/innerModExport2.errors.txt
+++ b/tests/baselines/reference/innerModExport2.errors.txt
@@ -1,7 +1,7 @@
 tests/cases/compiler/innerModExport2.ts(5,5): error TS2304: Cannot find name 'module'.
 tests/cases/compiler/innerModExport2.ts(5,12): error TS1005: ';' expected.
-tests/cases/compiler/innerModExport2.ts(7,20): error TS2395: Individual declarations in merged declaration export_var must be all exported or all local.
-tests/cases/compiler/innerModExport2.ts(13,9): error TS2395: Individual declarations in merged declaration export_var must be all exported or all local.
+tests/cases/compiler/innerModExport2.ts(7,20): error TS2395: Individual declarations in merged declaration 'export_var' must be all exported or all local.
+tests/cases/compiler/innerModExport2.ts(13,9): error TS2395: Individual declarations in merged declaration 'export_var' must be all exported or all local.
 tests/cases/compiler/innerModExport2.ts(20,7): error TS2339: Property 'NonExportFunc' does not exist on type 'typeof Outer'.
 
 
@@ -18,7 +18,7 @@ tests/cases/compiler/innerModExport2.ts(20,7): error TS2339: Property 'NonExport
             var non_export_var = 0;
             export var export_var = 1;
                        ~~~~~~~~~~
-!!! error TS2395: Individual declarations in merged declaration export_var must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'export_var' must be all exported or all local.
     
             function NonExportFunc() { return 0; }
     
@@ -26,7 +26,7 @@ tests/cases/compiler/innerModExport2.ts(20,7): error TS2339: Property 'NonExport
         }
         var export_var: number;
             ~~~~~~~~~~
-!!! error TS2395: Individual declarations in merged declaration export_var must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'export_var' must be all exported or all local.
     
         export var outer_var_export = 0;
         export function outerFuncExport() { return 0; }
diff --git a/tests/baselines/reference/multipleDefaultExports01.errors.txt b/tests/baselines/reference/multipleDefaultExports01.errors.txt
new file mode 100644
index 00000000000..7b49afe1a4e
--- /dev/null
+++ b/tests/baselines/reference/multipleDefaultExports01.errors.txt
@@ -0,0 +1,31 @@
+tests/cases/conformance/es6/modules/m1.ts(2,22): error TS2300: Duplicate identifier 'foo'.
+tests/cases/conformance/es6/modules/m1.ts(6,25): error TS2300: Duplicate identifier 'bar'.
+tests/cases/conformance/es6/modules/m1.ts(11,1): error TS2300: Duplicate identifier 'default'.
+tests/cases/conformance/es6/modules/m2.ts(3,1): error TS2348: Value of type 'typeof foo' is not callable. Did you mean to include 'new'?
+
+
+==== tests/cases/conformance/es6/modules/m1.ts (3 errors) ====
+    
+    export default class foo {
+                         ~~~
+!!! error TS2300: Duplicate identifier 'foo'.
+    
+    }
+    
+    export default function bar() {
+                            ~~~
+!!! error TS2300: Duplicate identifier 'bar'.
+    
+    }
+    
+    var x = 10;
+    export default x;
+    ~~~~~~~~~~~~~~~~~
+!!! error TS2300: Duplicate identifier 'default'.
+    
+==== tests/cases/conformance/es6/modules/m2.ts (1 errors) ====
+    import Entity from "m1"
+    
+    Entity();
+    ~~~~~~~~
+!!! error TS2348: Value of type 'typeof foo' is not callable. Did you mean to include 'new'?
\ No newline at end of file
diff --git a/tests/baselines/reference/multipleDefaultExports01.js b/tests/baselines/reference/multipleDefaultExports01.js
new file mode 100644
index 00000000000..e633cf69f55
--- /dev/null
+++ b/tests/baselines/reference/multipleDefaultExports01.js
@@ -0,0 +1,38 @@
+//// [tests/cases/conformance/es6/modules/multipleDefaultExports01.ts] ////
+
+//// [m1.ts]
+
+export default class foo {
+
+}
+
+export default function bar() {
+
+}
+
+var x = 10;
+export default x;
+
+//// [m2.ts]
+import Entity from "m1"
+
+Entity();
+
+//// [m1.js]
+var foo = (function () {
+    function foo() {
+    }
+    return foo;
+})();
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = foo;
+function bar() {
+}
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = bar;
+var x = 10;
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = x;
+//// [m2.js]
+var m1_1 = require("m1");
+m1_1.default();
diff --git a/tests/baselines/reference/multipleDefaultExports02.errors.txt b/tests/baselines/reference/multipleDefaultExports02.errors.txt
new file mode 100644
index 00000000000..51220ecfae2
--- /dev/null
+++ b/tests/baselines/reference/multipleDefaultExports02.errors.txt
@@ -0,0 +1,22 @@
+tests/cases/conformance/es6/modules/m1.ts(2,25): error TS2393: Duplicate function implementation.
+tests/cases/conformance/es6/modules/m1.ts(6,25): error TS2393: Duplicate function implementation.
+
+
+==== tests/cases/conformance/es6/modules/m1.ts (2 errors) ====
+    
+    export default function foo() {
+                            ~~~
+!!! error TS2393: Duplicate function implementation.
+    
+    }
+    
+    export default function bar() {
+                            ~~~
+!!! error TS2393: Duplicate function implementation.
+    
+    }
+    
+==== tests/cases/conformance/es6/modules/m2.ts (0 errors) ====
+    import Entity from "m1"
+    
+    Entity();
\ No newline at end of file
diff --git a/tests/baselines/reference/multipleDefaultExports02.js b/tests/baselines/reference/multipleDefaultExports02.js
new file mode 100644
index 00000000000..3d1b84ff6a6
--- /dev/null
+++ b/tests/baselines/reference/multipleDefaultExports02.js
@@ -0,0 +1,29 @@
+//// [tests/cases/conformance/es6/modules/multipleDefaultExports02.ts] ////
+
+//// [m1.ts]
+
+export default function foo() {
+
+}
+
+export default function bar() {
+
+}
+
+//// [m2.ts]
+import Entity from "m1"
+
+Entity();
+
+//// [m1.js]
+function foo() {
+}
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = foo;
+function bar() {
+}
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.default = bar;
+//// [m2.js]
+var m1_1 = require("m1");
+m1_1.default();
diff --git a/tests/baselines/reference/multivar.errors.txt b/tests/baselines/reference/multivar.errors.txt
index 931e61de5ae..44061b9d74c 100644
--- a/tests/baselines/reference/multivar.errors.txt
+++ b/tests/baselines/reference/multivar.errors.txt
@@ -1,5 +1,5 @@
-tests/cases/compiler/multivar.ts(6,19): error TS2395: Individual declarations in merged declaration b2 must be all exported or all local.
-tests/cases/compiler/multivar.ts(22,9): error TS2395: Individual declarations in merged declaration b2 must be all exported or all local.
+tests/cases/compiler/multivar.ts(6,19): error TS2395: Individual declarations in merged declaration 'b2' must be all exported or all local.
+tests/cases/compiler/multivar.ts(22,9): error TS2395: Individual declarations in merged declaration 'b2' must be all exported or all local.
 
 
 ==== tests/cases/compiler/multivar.ts (2 errors) ====
@@ -10,7 +10,7 @@ tests/cases/compiler/multivar.ts(22,9): error TS2395: Individual declarations in
     
         export var a, b2: number = 10, b;
                       ~~
-!!! error TS2395: Individual declarations in merged declaration b2 must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'b2' must be all exported or all local.
         var m1;
         var a2, b22: number = 10, b222;
         var m3;
@@ -28,7 +28,7 @@ tests/cases/compiler/multivar.ts(22,9): error TS2395: Individual declarations in
         declare var d1, d2;
         var b2;
             ~~
-!!! error TS2395: Individual declarations in merged declaration b2 must be all exported or all local.
+!!! error TS2395: Individual declarations in merged declaration 'b2' must be all exported or all local.
     
         declare var v1;
     }
diff --git a/tests/cases/conformance/es6/modules/defaultExportsCannotMerge01.ts b/tests/cases/conformance/es6/modules/defaultExportsCannotMerge01.ts
new file mode 100644
index 00000000000..7caa9caf574
--- /dev/null
+++ b/tests/cases/conformance/es6/modules/defaultExportsCannotMerge01.ts
@@ -0,0 +1,31 @@
+// @module: commonjs
+// @target: ES5
+
+// @filename: m1.ts
+export default function Decl() {
+    return 0;
+}
+
+export interface Decl {
+    p1: number;
+    p2: number;
+}
+
+export namespace Decl {
+    export var x = 10;
+    export var y = 20;
+
+    interface I {
+    }
+}
+
+// @filename: m2.ts
+import Entity from "m1"
+
+Entity();
+
+var x: Entity;
+var y: Entity.I;
+
+Entity.x;
+Entity.y;
\ No newline at end of file
diff --git a/tests/cases/conformance/es6/modules/defaultExportsCannotMerge02.ts b/tests/cases/conformance/es6/modules/defaultExportsCannotMerge02.ts
new file mode 100644
index 00000000000..f7312ec2e66
--- /dev/null
+++ b/tests/cases/conformance/es6/modules/defaultExportsCannotMerge02.ts
@@ -0,0 +1,26 @@
+// @module: commonjs
+// @target: ES5
+
+// @filename: m1.ts
+export default class Decl {
+}
+
+export interface Decl {
+    p1: number;
+    p2: number;
+}
+
+export namespace Decl {
+    interface I {
+    }
+}
+
+// @filename: m2.ts
+import Entity from "m1"
+
+Entity();
+
+var x: Entity;
+var y: Entity.I;
+var z = new Entity();
+var sum = z.p1 + z.p2
\ No newline at end of file
diff --git a/tests/cases/conformance/es6/modules/defaultExportsCannotMerge03.ts b/tests/cases/conformance/es6/modules/defaultExportsCannotMerge03.ts
new file mode 100644
index 00000000000..dad8431812b
--- /dev/null
+++ b/tests/cases/conformance/es6/modules/defaultExportsCannotMerge03.ts
@@ -0,0 +1,26 @@
+// @module: commonjs
+// @target: ES5
+
+// @filename: m1.ts
+export default class Decl {
+}
+
+interface Decl {
+    p1: number;
+    p2: number;
+}
+
+namespace Decl {
+    interface I {
+    }
+}
+
+// @filename: m2.ts
+import Entity from "m1"
+
+Entity();
+
+var x: Entity;
+var y: Entity.I;
+var z = new Entity();
+var sum = z.p1 + z.p2
\ No newline at end of file
diff --git a/tests/cases/conformance/es6/modules/defaultExportsCannotMerge04.ts b/tests/cases/conformance/es6/modules/defaultExportsCannotMerge04.ts
new file mode 100644
index 00000000000..ab72d10504a
--- /dev/null
+++ b/tests/cases/conformance/es6/modules/defaultExportsCannotMerge04.ts
@@ -0,0 +1,15 @@
+// @module: commonjs
+// @target: ES5
+
+export default function Foo() {
+}
+
+namespace Foo {
+    export var x;
+}
+
+interface Foo {
+}
+
+export interface Foo {
+}
\ No newline at end of file
diff --git a/tests/cases/conformance/es6/modules/multipleDefaultExports01.ts b/tests/cases/conformance/es6/modules/multipleDefaultExports01.ts
new file mode 100644
index 00000000000..84172248e93
--- /dev/null
+++ b/tests/cases/conformance/es6/modules/multipleDefaultExports01.ts
@@ -0,0 +1,19 @@
+// @module: commonjs
+// @target: ES5
+
+// @filename: m1.ts
+export default class foo {
+
+}
+
+export default function bar() {
+
+}
+
+var x = 10;
+export default x;
+
+// @filename: m2.ts
+import Entity from "m1"
+
+Entity();
\ No newline at end of file
diff --git a/tests/cases/conformance/es6/modules/multipleDefaultExports02.ts b/tests/cases/conformance/es6/modules/multipleDefaultExports02.ts
new file mode 100644
index 00000000000..1e9c8dabc13
--- /dev/null
+++ b/tests/cases/conformance/es6/modules/multipleDefaultExports02.ts
@@ -0,0 +1,16 @@
+// @module: commonjs
+// @target: ES5
+
+// @filename: m1.ts
+export default function foo() {
+
+}
+
+export default function bar() {
+
+}
+
+// @filename: m2.ts
+import Entity from "m1"
+
+Entity();
\ No newline at end of file