diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 36f9bbb654b..c864a8aa76a 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -5365,25 +5365,25 @@ module ts {
                     }
                 }
                 // Target type is type of constructor signiture
-                let constructorSignitures: Signature[];
+                let constructSignitures: Signature[];
                 if (rightType.flags & TypeFlags.Interface) {
-                    constructorSignitures = (<InterfaceTypeWithDeclaredMembers>rightType).declaredConstructSignatures;
+                    constructSignitures = (<InterfaceTypeWithDeclaredMembers>rightType).declaredConstructSignatures;
                 }
                 if (rightType.flags & TypeFlags.Anonymous) {
-                    constructorSignitures = (<ResolvedType>rightType).constructSignatures;
+                    constructSignitures = (<ResolvedType>rightType).constructSignatures;
                 }
-                if (constructorSignitures) {
-                    let constructorType = getUnionType(map(constructorSignitures, constructorSignature => {
-                        if (constructorSignature.typeParameters && constructorSignature.typeParameters.length !== 0) {
-                            // TODO convert type parameters to any or empty object types. e.g. Sample<T> -> Sample<any> or Sample<{}>.
+                if (constructSignitures) {
+                    let instanceType = getUnionType(map(constructSignitures, constructSignature => {
+                        if (constructSignature.typeParameters && constructSignature.typeParameters.length !== 0) {
+                            constructSignature = instantiateSignature(constructSignature, createTypeMapper(constructSignature.typeParameters, map(constructSignature.typeParameters, _ => anyType)), true)
                         }
-                        return constructorSignature.resolvedReturnType;
+                        return constructSignature.resolvedReturnType;
                     }));
                     // Pickup type from union types
                     if (type.flags & TypeFlags.Union) {
-                        return getUnionType(filter((<UnionType>type).types, t => isTypeSubtypeOf(t, constructorType)));
+                        return getUnionType(filter((<UnionType>type).types, t => isTypeSubtypeOf(t, instanceType)));
                     }
-                    return constructorType;
+                    return instanceType;
                 }
                 return type;
             }
diff --git a/tests/baselines/reference/typeGuardsWithInstanceOfByConstructorSignature.errors.txt b/tests/baselines/reference/typeGuardsWithInstanceOfByConstructorSignature.errors.txt
index c7146541705..1816ef77fc2 100644
--- a/tests/baselines/reference/typeGuardsWithInstanceOfByConstructorSignature.errors.txt
+++ b/tests/baselines/reference/typeGuardsWithInstanceOfByConstructorSignature.errors.txt
@@ -1,12 +1,16 @@
 tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(12,10): error TS2339: Property 'bar' does not exist on type 'A'.
-tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(32,10): error TS2339: Property 'foo' does not exist on type '{}'.
-tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(33,10): error TS2339: Property 'foo' does not exist on type '{}'.
-tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(34,10): error TS2339: Property 'bar' does not exist on type '{}'.
+tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(33,5): error TS2322: Type 'string' is not assignable to type 'number'.
+tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(34,10): error TS2339: Property 'bar' does not exist on type 'B<number>'.
 tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(63,10): error TS2339: Property 'bar2' does not exist on type 'C1'.
 tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(82,10): error TS2339: Property 'bar' does not exist on type 'D'.
+tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(109,10): error TS2339: Property 'bar2' does not exist on type 'E1'.
+tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(131,11): error TS2339: Property 'foo' does not exist on type 'string | F'.
+tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(132,11): error TS2339: Property 'bar' does not exist on type 'string | F'.
+tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(157,11): error TS2339: Property 'foo2' does not exist on type 'G1'.
+tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts(179,11): error TS2339: Property 'bar' does not exist on type 'H'.
 
 
-==== tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts (6 errors) ====
+==== tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts (10 errors) ====
     interface AConstructor {
         new (): A;
     }
@@ -29,7 +33,7 @@ tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstru
         obj2.bar;
     }
     
-    // with generics
+    // a construct signature with generics
     interface BConstructor {
         new <T>(): B<T>;
     }
@@ -38,17 +42,15 @@ tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstru
     }
     declare var B: BConstructor;
     
-    var obj3: B<string> | A;
-    if (obj3 instanceof B) { // narrowed to B<string>.
-        obj3.foo = "str";
-             ~~~
-!!! error TS2339: Property 'foo' does not exist on type '{}'.
+    var obj3: B<number> | string;
+    if (obj3 instanceof B) { // narrowed to B<number>.
         obj3.foo = 1;
-             ~~~
-!!! error TS2339: Property 'foo' does not exist on type '{}'.
+        obj3.foo = "str";
+        ~~~~~~~~
+!!! error TS2322: Type 'string' is not assignable to type 'number'.
         obj3.bar = "str";
              ~~~
-!!! error TS2339: Property 'bar' does not exist on type '{}'.
+!!! error TS2339: Property 'bar' does not exist on type 'B<number>'.
     }
     
     var obj4: any;
@@ -58,7 +60,7 @@ tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstru
         obj4.bar = "str";
     }
     
-    // has multiple constructor signature
+    // has multiple construct signature
     interface CConstructor {
         new (value: string): C1;
         new (value: number): C2;
@@ -108,4 +110,111 @@ tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstru
         obj8.foo;
         obj8.bar;
     }
+    
+    // a construct signature that returns a union type
+    interface EConstructor {
+        new (): E1 | E2;
+    }
+    interface E1 {
+        foo: string;
+        bar1: number;
+    }
+    interface E2 {
+        foo: string;
+        bar2: number;
+    }
+    declare var E: EConstructor;
+    
+    var obj9: E1 | A;
+    if (obj9 instanceof E) { // narrowed to E1.
+        obj9.foo;
+        obj9.bar1;
+        obj9.bar2;
+             ~~~~
+!!! error TS2339: Property 'bar2' does not exist on type 'E1'.
+    }
+    
+    var obj10: any;
+    if (obj10 instanceof E) { // can't type narrowing from any.
+        obj10.foo;
+        obj10.bar1;
+        obj10.bar2;
+    }
+    
+    // a construct signature that returns any
+    interface FConstructor {
+        new (): any;
+    }
+    interface F {
+        foo: string;
+        bar: number;
+    }
+    declare var F: FConstructor;
+    
+    var obj11: F | string;
+    if (obj11 instanceof F) { // can't type narrowing, construct signiture returns any.
+        obj11.foo;
+              ~~~
+!!! error TS2339: Property 'foo' does not exist on type 'string | F'.
+        obj11.bar;
+              ~~~
+!!! error TS2339: Property 'bar' does not exist on type 'string | F'.
+    }
+    
+    var obj12: any;
+    if (obj12 instanceof F) { // can't type narrowing from any.
+        obj12.foo;
+        obj12.bar;
+    }
+    
+    // a type with a prototype, it overrides the construct signiture
+    interface GConstructor {
+        prototype: G1; // high priority
+        new (): G2;    // low priority
+    }
+    interface G1 {
+        foo1: number;
+    }
+    interface G2 {
+        foo2: boolean;
+    }
+    declare var G: GConstructor;
+    
+    var obj13: G1 | G2;
+    if (obj13 instanceof G) { // narrowed to G1. G1 is return type of prototype property.
+        obj13.foo1;
+        obj13.foo2;
+              ~~~~
+!!! error TS2339: Property 'foo2' does not exist on type 'G1'.
+    }
+    
+    var obj14: any;
+    if (obj14 instanceof G) { // can't type narrowing from any.
+        obj14.foo1;
+        obj14.foo2;
+    }
+    
+    // a type with a prototype that has any type
+    interface HConstructor {
+        prototype: any; // high priority, but any type is ignored. interface has implicit `prototype: any`.
+        new (): H;      // low priority
+    }
+    interface H {
+        foo: number;
+    }
+    declare var H: HConstructor;
+    
+    var obj15: H | string;
+    if (obj15 instanceof H) { // narrowed to H.
+        obj15.foo;
+        obj15.bar;
+              ~~~
+!!! error TS2339: Property 'bar' does not exist on type 'H'.
+    }
+    
+    var obj16: any;
+    if (obj16 instanceof H) { // can't type narrowing from any.
+        obj16.foo1;
+        obj16.foo2;
+    }
     
\ No newline at end of file
diff --git a/tests/baselines/reference/typeGuardsWithInstanceOfByConstructorSignature.js b/tests/baselines/reference/typeGuardsWithInstanceOfByConstructorSignature.js
index c795126b0ff..395a5e96e05 100644
--- a/tests/baselines/reference/typeGuardsWithInstanceOfByConstructorSignature.js
+++ b/tests/baselines/reference/typeGuardsWithInstanceOfByConstructorSignature.js
@@ -19,7 +19,7 @@ if (obj2 instanceof A) { // can't type narrowing from any.
     obj2.bar;
 }
 
-// with generics
+// a construct signature with generics
 interface BConstructor {
     new <T>(): B<T>;
 }
@@ -28,10 +28,10 @@ interface B<T> {
 }
 declare var B: BConstructor;
 
-var obj3: B<string> | A;
-if (obj3 instanceof B) { // narrowed to B<string>.
-    obj3.foo = "str";
+var obj3: B<number> | string;
+if (obj3 instanceof B) { // narrowed to B<number>.
     obj3.foo = 1;
+    obj3.foo = "str";
     obj3.bar = "str";
 }
 
@@ -42,7 +42,7 @@ if (obj4 instanceof B) { // can't type narrowing from any.
     obj4.bar = "str";
 }
 
-// has multiple constructor signature
+// has multiple construct signature
 interface CConstructor {
     new (value: string): C1;
     new (value: number): C2;
@@ -89,6 +89,103 @@ if (obj8 instanceof D) { // can't type narrowing from any.
     obj8.bar;
 }
 
+// a construct signature that returns a union type
+interface EConstructor {
+    new (): E1 | E2;
+}
+interface E1 {
+    foo: string;
+    bar1: number;
+}
+interface E2 {
+    foo: string;
+    bar2: number;
+}
+declare var E: EConstructor;
+
+var obj9: E1 | A;
+if (obj9 instanceof E) { // narrowed to E1.
+    obj9.foo;
+    obj9.bar1;
+    obj9.bar2;
+}
+
+var obj10: any;
+if (obj10 instanceof E) { // can't type narrowing from any.
+    obj10.foo;
+    obj10.bar1;
+    obj10.bar2;
+}
+
+// a construct signature that returns any
+interface FConstructor {
+    new (): any;
+}
+interface F {
+    foo: string;
+    bar: number;
+}
+declare var F: FConstructor;
+
+var obj11: F | string;
+if (obj11 instanceof F) { // can't type narrowing, construct signiture returns any.
+    obj11.foo;
+    obj11.bar;
+}
+
+var obj12: any;
+if (obj12 instanceof F) { // can't type narrowing from any.
+    obj12.foo;
+    obj12.bar;
+}
+
+// a type with a prototype, it overrides the construct signiture
+interface GConstructor {
+    prototype: G1; // high priority
+    new (): G2;    // low priority
+}
+interface G1 {
+    foo1: number;
+}
+interface G2 {
+    foo2: boolean;
+}
+declare var G: GConstructor;
+
+var obj13: G1 | G2;
+if (obj13 instanceof G) { // narrowed to G1. G1 is return type of prototype property.
+    obj13.foo1;
+    obj13.foo2;
+}
+
+var obj14: any;
+if (obj14 instanceof G) { // can't type narrowing from any.
+    obj14.foo1;
+    obj14.foo2;
+}
+
+// a type with a prototype that has any type
+interface HConstructor {
+    prototype: any; // high priority, but any type is ignored. interface has implicit `prototype: any`.
+    new (): H;      // low priority
+}
+interface H {
+    foo: number;
+}
+declare var H: HConstructor;
+
+var obj15: H | string;
+if (obj15 instanceof H) { // narrowed to H.
+    obj15.foo;
+    obj15.bar;
+}
+
+var obj16: any;
+if (obj16 instanceof H) { // can't type narrowing from any.
+    obj16.foo1;
+    obj16.foo2;
+}
+
 
 //// [typeGuardsWithInstanceOfByConstructorSignature.js]
 var obj1;
@@ -103,8 +200,8 @@ if (obj2 instanceof A) {
 }
 var obj3;
 if (obj3 instanceof B) {
-    obj3.foo = "str";
     obj3.foo = 1;
+    obj3.foo = "str";
     obj3.bar = "str";
 }
 var obj4;
@@ -135,3 +232,45 @@ if (obj8 instanceof D) {
     obj8.foo;
     obj8.bar;
 }
+var obj9;
+if (obj9 instanceof E) {
+    obj9.foo;
+    obj9.bar1;
+    obj9.bar2;
+}
+var obj10;
+if (obj10 instanceof E) {
+    obj10.foo;
+    obj10.bar1;
+    obj10.bar2;
+}
+var obj11;
+if (obj11 instanceof F) {
+    obj11.foo;
+    obj11.bar;
+}
+var obj12;
+if (obj12 instanceof F) {
+    obj12.foo;
+    obj12.bar;
+}
+var obj13;
+if (obj13 instanceof G) {
+    obj13.foo1;
+    obj13.foo2;
+}
+var obj14;
+if (obj14 instanceof G) {
+    obj14.foo1;
+    obj14.foo2;
+}
+var obj15;
+if (obj15 instanceof H) {
+    obj15.foo;
+    obj15.bar;
+}
+var obj16;
+if (obj16 instanceof H) {
+    obj16.foo1;
+    obj16.foo2;
+}
diff --git a/tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts b/tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts
index b28d92e2c8e..c432ceb2bda 100644
--- a/tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts
+++ b/tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts
@@ -18,7 +18,7 @@ if (obj2 instanceof A) { // can't type narrowing from any.
     obj2.bar;
 }
 
-// with generics
+// a construct signature with generics
 interface BConstructor {
     new <T>(): B<T>;
 }
@@ -27,10 +27,10 @@ interface B<T> {
 }
 declare var B: BConstructor;
 
-var obj3: B<string> | A;
-if (obj3 instanceof B) { // narrowed to B<string>.
-    obj3.foo = "str";
+var obj3: B<number> | string;
+if (obj3 instanceof B) { // narrowed to B<number>.
     obj3.foo = 1;
+    obj3.foo = "str";
     obj3.bar = "str";
 }
 
@@ -41,7 +41,7 @@ if (obj4 instanceof B) { // can't type narrowing from any.
     obj4.bar = "str";
 }
 
-// has multiple constructor signature
+// has multiple construct signature
 interface CConstructor {
     new (value: string): C1;
     new (value: number): C2;
@@ -87,3 +87,100 @@ if (obj8 instanceof D) { // can't type narrowing from any.
     obj8.foo;
     obj8.bar;
 }
+
+// a construct signature that returns a union type
+interface EConstructor {
+    new (): E1 | E2;
+}
+interface E1 {
+    foo: string;
+    bar1: number;
+}
+interface E2 {
+    foo: string;
+    bar2: number;
+}
+declare var E: EConstructor;
+
+var obj9: E1 | A;
+if (obj9 instanceof E) { // narrowed to E1.
+    obj9.foo;
+    obj9.bar1;
+    obj9.bar2;
+}
+
+var obj10: any;
+if (obj10 instanceof E) { // can't type narrowing from any.
+    obj10.foo;
+    obj10.bar1;
+    obj10.bar2;
+}
+
+// a construct signature that returns any
+interface FConstructor {
+    new (): any;
+}
+interface F {
+    foo: string;
+    bar: number;
+}
+declare var F: FConstructor;
+
+var obj11: F | string;
+if (obj11 instanceof F) { // can't type narrowing, construct signiture returns any.
+    obj11.foo;
+    obj11.bar;
+}
+
+var obj12: any;
+if (obj12 instanceof F) { // can't type narrowing from any.
+    obj12.foo;
+    obj12.bar;
+}
+
+// a type with a prototype, it overrides the construct signiture
+interface GConstructor {
+    prototype: G1; // high priority
+    new (): G2;    // low priority
+}
+interface G1 {
+    foo1: number;
+}
+interface G2 {
+    foo2: boolean;
+}
+declare var G: GConstructor;
+
+var obj13: G1 | G2;
+if (obj13 instanceof G) { // narrowed to G1. G1 is return type of prototype property.
+    obj13.foo1;
+    obj13.foo2;
+}
+
+var obj14: any;
+if (obj14 instanceof G) { // can't type narrowing from any.
+    obj14.foo1;
+    obj14.foo2;
+}
+
+// a type with a prototype that has any type
+interface HConstructor {
+    prototype: any; // high priority, but any type is ignored. interface has implicit `prototype: any`.
+    new (): H;      // low priority
+}
+interface H {
+    foo: number;
+}
+declare var H: HConstructor;
+
+var obj15: H | string;
+if (obj15 instanceof H) { // narrowed to H.
+    obj15.foo;
+    obj15.bar;
+}
+
+var obj16: any;
+if (obj16 instanceof H) { // can't type narrowing from any.
+    obj16.foo1;
+    obj16.foo2;
+}