diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index f3604ab49ba..a3ce22bbed1 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -3634,6 +3634,10 @@ module ts {
             return type;
         }
 
+        function getUnionTypeOfSubtypeConstituents(source: UnionType, target: Type): Type {
+            return getUnionType(filter(source.types, t => isTypeSubtypeOf(t, target)));
+        }
+
         function getReducedTypeOfUnionType(type: UnionType): Type {
             // If union type was created without subtype reduction, perform the deferred reduction now
             if (!type.reducedType) {
@@ -5386,17 +5390,35 @@ module ts {
                 }
                 // Target type is type of prototype property
                 let prototypeProperty = getPropertyOfType(rightType, "prototype");
-                if (!prototypeProperty) {
-                    return type;
+                if (prototypeProperty) {
+                    let targetType = getTypeOfSymbol(prototypeProperty);
+                    if (targetType !== anyType) {
+                        // Narrow to the target type if it's a subtype of the current type
+                        if (isTypeSubtypeOf(targetType, type)) {
+                            return targetType;
+                        }
+                        // If the current type is a union type, remove all constituents that aren't subtypes of the target.
+                        if (type.flags & TypeFlags.Union) {
+                            return getUnionTypeOfSubtypeConstituents(<UnionType>type, targetType);
+                        }
+                    }
                 }
-                let targetType = getTypeOfSymbol(prototypeProperty);
-                // Narrow to target type if it is a subtype of current type
-                if (isTypeSubtypeOf(targetType, type)) {
-                    return targetType;
+                // Target type is type of construct signature
+                let constructSignatures: Signature[];
+                if (rightType.flags & TypeFlags.Interface) {
+                    constructSignatures = resolveDeclaredMembers(<InterfaceType>rightType).declaredConstructSignatures;
                 }
-                // If current type is a union type, remove all constituents that aren't subtypes of target type
-                if (type.flags & TypeFlags.Union) {
-                    return getUnionType(filter((<UnionType>type).types, t => isTypeSubtypeOf(t, targetType)));
+                else if (rightType.flags & TypeFlags.Anonymous) {
+                    constructSignatures = getSignaturesOfType(rightType, SignatureKind.Construct);
+                }
+
+                if (constructSignatures && constructSignatures.length !== 0) {
+                    let instanceType = getUnionType(map(constructSignatures, signature => getReturnTypeOfSignature(getErasedSignature(signature))));
+                    // Pickup type from union types
+                    if (type.flags & TypeFlags.Union) {
+                        return getUnionTypeOfSubtypeConstituents(<UnionType>type, instanceType);
+                    }
+                    return instanceType;
                 }
                 return type;
             }
diff --git a/tests/baselines/reference/typeGuardsWithInstanceOfByConstructorSignature.errors.txt b/tests/baselines/reference/typeGuardsWithInstanceOfByConstructorSignature.errors.txt
new file mode 100644
index 00000000000..b963b2c33ae
--- /dev/null
+++ b/tests/baselines/reference/typeGuardsWithInstanceOfByConstructorSignature.errors.txt
@@ -0,0 +1,220 @@
+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(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 (10 errors) ====
+    interface AConstructor {
+        new (): A;
+    }
+    interface A {
+        foo: string;
+    }
+    declare var A: AConstructor;
+    
+    var obj1: A | string;
+    if (obj1 instanceof A) { // narrowed to A.
+        obj1.foo;
+        obj1.bar;
+             ~~~
+!!! error TS2339: Property 'bar' does not exist on type 'A'.
+    }
+    
+    var obj2: any;
+    if (obj2 instanceof A) { // can't narrow type from 'any'
+        obj2.foo;
+        obj2.bar;
+    }
+    
+    // a construct signature with generics
+    interface BConstructor {
+        new <T>(): B<T>;
+    }
+    interface B<T> {
+        foo: T;
+    }
+    declare var B: BConstructor;
+    
+    var obj3: B<number> | string;
+    if (obj3 instanceof B) { // narrowed to B<number>.
+        obj3.foo = 1;
+        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 'B<number>'.
+    }
+    
+    var obj4: any;
+    if (obj4 instanceof B) { // can't narrow type from 'any'
+        obj4.foo = "str";
+        obj4.foo = 1;
+        obj4.bar = "str";
+    }
+    
+    // has multiple construct signature
+    interface CConstructor {
+        new (value: string): C1;
+        new (value: number): C2;
+    }
+    interface C1 {
+        foo: string;
+        bar1: number;
+    }
+    interface C2 {
+        foo: string;
+        bar2: number;
+    }
+    declare var C: CConstructor;
+    
+    var obj5: C1 | A;
+    if (obj5 instanceof C) { // narrowed to C1.
+        obj5.foo;
+        obj5.bar1;
+        obj5.bar2;
+             ~~~~
+!!! error TS2339: Property 'bar2' does not exist on type 'C1'.
+    }
+    
+    var obj6: any;
+    if (obj6 instanceof C) { // can't narrow type from 'any'
+        obj6.foo;
+        obj6.bar1;
+        obj6.bar2;
+    }
+    
+    // with object type literal
+    interface D {
+        foo: string;
+    }
+    declare var D: { new (): D; };
+    
+    var obj7: D | string;
+    if (obj7 instanceof D) { // narrowed to D.
+        obj7.foo;
+        obj7.bar;
+             ~~~
+!!! error TS2339: Property 'bar' does not exist on type 'D'.
+    }
+    
+    var obj8: any;
+    if (obj8 instanceof D) { // can't narrow type 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;
+             ~~~~
+!!! error TS2339: Property 'bar2' does not exist on type 'E1'.
+    }
+    
+    var obj10: any;
+    if (obj10 instanceof E) { // can't narrow type 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 signature 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 narrow type from 'any'
+        obj12.foo;
+        obj12.bar;
+    }
+    
+    // a type with a prototype, it overrides the construct signature
+    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 narrow type 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 narrow type 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
new file mode 100644
index 00000000000..e5b12bacb1f
--- /dev/null
+++ b/tests/baselines/reference/typeGuardsWithInstanceOfByConstructorSignature.js
@@ -0,0 +1,276 @@
+//// [typeGuardsWithInstanceOfByConstructorSignature.ts]
+interface AConstructor {
+    new (): A;
+}
+interface A {
+    foo: string;
+}
+declare var A: AConstructor;
+
+var obj1: A | string;
+if (obj1 instanceof A) { // narrowed to A.
+    obj1.foo;
+    obj1.bar;
+}
+
+var obj2: any;
+if (obj2 instanceof A) { // can't narrow type from 'any'
+    obj2.foo;
+    obj2.bar;
+}
+
+// a construct signature with generics
+interface BConstructor {
+    new <T>(): B<T>;
+}
+interface B<T> {
+    foo: T;
+}
+declare var B: BConstructor;
+
+var obj3: B<number> | string;
+if (obj3 instanceof B) { // narrowed to B<number>.
+    obj3.foo = 1;
+    obj3.foo = "str";
+    obj3.bar = "str";
+}
+
+var obj4: any;
+if (obj4 instanceof B) { // can't narrow type from 'any'
+    obj4.foo = "str";
+    obj4.foo = 1;
+    obj4.bar = "str";
+}
+
+// has multiple construct signature
+interface CConstructor {
+    new (value: string): C1;
+    new (value: number): C2;
+}
+interface C1 {
+    foo: string;
+    bar1: number;
+}
+interface C2 {
+    foo: string;
+    bar2: number;
+}
+declare var C: CConstructor;
+
+var obj5: C1 | A;
+if (obj5 instanceof C) { // narrowed to C1.
+    obj5.foo;
+    obj5.bar1;
+    obj5.bar2;
+}
+
+var obj6: any;
+if (obj6 instanceof C) { // can't narrow type from 'any'
+    obj6.foo;
+    obj6.bar1;
+    obj6.bar2;
+}
+
+// with object type literal
+interface D {
+    foo: string;
+}
+declare var D: { new (): D; };
+
+var obj7: D | string;
+if (obj7 instanceof D) { // narrowed to D.
+    obj7.foo;
+    obj7.bar;
+}
+
+var obj8: any;
+if (obj8 instanceof D) { // can't narrow type 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 narrow type 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 signature returns any.
+    obj11.foo;
+    obj11.bar;
+}
+
+var obj12: any;
+if (obj12 instanceof F) { // can't narrow type from 'any'
+    obj12.foo;
+    obj12.bar;
+}
+
+// a type with a prototype, it overrides the construct signature
+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 narrow type 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 narrow type from 'any'
+    obj16.foo1;
+    obj16.foo2;
+}
+
+
+//// [typeGuardsWithInstanceOfByConstructorSignature.js]
+var obj1;
+if (obj1 instanceof A) {
+    obj1.foo;
+    obj1.bar;
+}
+var obj2;
+if (obj2 instanceof A) {
+    obj2.foo;
+    obj2.bar;
+}
+var obj3;
+if (obj3 instanceof B) {
+    obj3.foo = 1;
+    obj3.foo = "str";
+    obj3.bar = "str";
+}
+var obj4;
+if (obj4 instanceof B) {
+    obj4.foo = "str";
+    obj4.foo = 1;
+    obj4.bar = "str";
+}
+var obj5;
+if (obj5 instanceof C) {
+    obj5.foo;
+    obj5.bar1;
+    obj5.bar2;
+}
+var obj6;
+if (obj6 instanceof C) {
+    obj6.foo;
+    obj6.bar1;
+    obj6.bar2;
+}
+var obj7;
+if (obj7 instanceof D) {
+    obj7.foo;
+    obj7.bar;
+}
+var obj8;
+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
new file mode 100644
index 00000000000..fee92ff10ca
--- /dev/null
+++ b/tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOfByConstructorSignature.ts
@@ -0,0 +1,186 @@
+interface AConstructor {
+    new (): A;
+}
+interface A {
+    foo: string;
+}
+declare var A: AConstructor;
+
+var obj1: A | string;
+if (obj1 instanceof A) { // narrowed to A.
+    obj1.foo;
+    obj1.bar;
+}
+
+var obj2: any;
+if (obj2 instanceof A) { // can't narrow type from 'any'
+    obj2.foo;
+    obj2.bar;
+}
+
+// a construct signature with generics
+interface BConstructor {
+    new <T>(): B<T>;
+}
+interface B<T> {
+    foo: T;
+}
+declare var B: BConstructor;
+
+var obj3: B<number> | string;
+if (obj3 instanceof B) { // narrowed to B<number>.
+    obj3.foo = 1;
+    obj3.foo = "str";
+    obj3.bar = "str";
+}
+
+var obj4: any;
+if (obj4 instanceof B) { // can't narrow type from 'any'
+    obj4.foo = "str";
+    obj4.foo = 1;
+    obj4.bar = "str";
+}
+
+// has multiple construct signature
+interface CConstructor {
+    new (value: string): C1;
+    new (value: number): C2;
+}
+interface C1 {
+    foo: string;
+    bar1: number;
+}
+interface C2 {
+    foo: string;
+    bar2: number;
+}
+declare var C: CConstructor;
+
+var obj5: C1 | A;
+if (obj5 instanceof C) { // narrowed to C1.
+    obj5.foo;
+    obj5.bar1;
+    obj5.bar2;
+}
+
+var obj6: any;
+if (obj6 instanceof C) { // can't narrow type from 'any'
+    obj6.foo;
+    obj6.bar1;
+    obj6.bar2;
+}
+
+// with object type literal
+interface D {
+    foo: string;
+}
+declare var D: { new (): D; };
+
+var obj7: D | string;
+if (obj7 instanceof D) { // narrowed to D.
+    obj7.foo;
+    obj7.bar;
+}
+
+var obj8: any;
+if (obj8 instanceof D) { // can't narrow type 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 narrow type 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 signature returns any.
+    obj11.foo;
+    obj11.bar;
+}
+
+var obj12: any;
+if (obj12 instanceof F) { // can't narrow type from 'any'
+    obj12.foo;
+    obj12.bar;
+}
+
+// a type with a prototype, it overrides the construct signature
+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 narrow type 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 narrow type from 'any'
+    obj16.foo1;
+    obj16.foo2;
+}