diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 6a45dacb32a..b0b6521e230 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -10417,7 +10417,7 @@ module ts {
 
             // Non-ambient classes cannot merge with interfaces.
             if (!(node.flags & NodeFlags.Ambient) && symbol.flags & SymbolFlags.Interface) {
-                error(node, Diagnostics.A_non_ambient_class_cannot_be_merged_with_an_interface)
+                error(node, Diagnostics.Only_an_ambient_class_can_be_merged_with_an_interface)
             }
 
             forEach(node.members, checkSourceElement);
@@ -10600,10 +10600,11 @@ module ts {
                     }
                 }
 
+                // Interfaces cannot merge with non-ambient classes.
                 if (symbol && symbol.declarations) {
                     for (let declaration of symbol.declarations) {
                         if (declaration.kind === SyntaxKind.ClassDeclaration && !(declaration.flags & NodeFlags.Ambient)) {
-                            error(node, Diagnostics.An_interface_cannot_merge_with_a_non_ambient_class);
+                            error(node, Diagnostics.Only_an_ambient_class_can_be_merged_with_an_interface);
                             break;
                         }
                     }
diff --git a/src/compiler/diagnosticInformationMap.generated.ts b/src/compiler/diagnosticInformationMap.generated.ts
index 358dea6e988..e327a516311 100644
--- a/src/compiler/diagnosticInformationMap.generated.ts
+++ b/src/compiler/diagnosticInformationMap.generated.ts
@@ -372,8 +372,7 @@ module ts {
         Cannot_find_namespace_0: { code: 2503, category: DiagnosticCategory.Error, key: "Cannot find namespace '{0}'." },
         No_best_common_type_exists_among_yield_expressions: { code: 2504, category: DiagnosticCategory.Error, key: "No best common type exists among yield expressions." },
         A_generator_cannot_have_a_void_type_annotation: { code: 2505, category: DiagnosticCategory.Error, key: "A generator cannot have a 'void' type annotation." },
-        A_non_ambient_class_cannot_be_merged_with_an_interface: { code: 2506, category: DiagnosticCategory.Error, key: "A non-ambient class cannot be merged with an interface." },
-        An_interface_cannot_merge_with_a_non_ambient_class: { code: 2507, category: DiagnosticCategory.Error, key: "An interface cannot merge with a non-ambient class." },
+        Only_an_ambient_class_can_be_merged_with_an_interface: { code: 2506, category: DiagnosticCategory.Error, key: "Only an ambient class can be merged with an interface." },
         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 8f3973fbdb8..871fb2d9ea8 100644
--- a/src/compiler/diagnosticMessages.json
+++ b/src/compiler/diagnosticMessages.json
@@ -1476,14 +1476,10 @@
         "category": "Error",
         "code": 2505
     },
-    "A non-ambient class cannot be merged with an interface.": {
+    "Only an ambient class can be merged with an interface.": {
         "category": "Error",
         "code": 2506
     },
-    "An interface cannot merge with a non-ambient class.": {
-        "category": "Error",
-        "code": 2507
-    },
     "Import declaration '{0}' is using private name '{1}'.": {
         "category": "Error",
         "code": 4000