diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 00990f0c8a..ca3c027640 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -4720,7 +4720,7 @@ module ts {
                     return targetType;
                 }
                 // If current type is a union type, remove all constituents that aren't subtypes of target type
-                if (type.flags && TypeFlags.Union) {
+                if (type.flags & TypeFlags.Union) {
                     return getUnionType(filter((<UnionType>type).types, t => isTypeSubtypeOf(t, targetType)));
                 }
                 return type;
diff --git a/tests/baselines/reference/typeGuardsWithInstanceOf.js b/tests/baselines/reference/typeGuardsWithInstanceOf.js
new file mode 100644
index 0000000000..34af7037f0
--- /dev/null
+++ b/tests/baselines/reference/typeGuardsWithInstanceOf.js
@@ -0,0 +1,18 @@
+//// [typeGuardsWithInstanceOf.ts]
+interface I { global: string; }
+var result: I;
+var result2: I;
+
+if (!(result instanceof RegExp)) {
+    result = result2;
+} else if (!result.global) {
+}
+
+//// [typeGuardsWithInstanceOf.js]
+var result;
+var result2;
+if (!(result instanceof RegExp)) {
+    result = result2;
+}
+else if (!result.global) {
+}
diff --git a/tests/baselines/reference/typeGuardsWithInstanceOf.types b/tests/baselines/reference/typeGuardsWithInstanceOf.types
new file mode 100644
index 0000000000..0d7b477fae
--- /dev/null
+++ b/tests/baselines/reference/typeGuardsWithInstanceOf.types
@@ -0,0 +1,31 @@
+=== tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOf.ts ===
+interface I { global: string; }
+>I : I
+>global : string
+
+var result: I;
+>result : I
+>I : I
+
+var result2: I;
+>result2 : I
+>I : I
+
+if (!(result instanceof RegExp)) {
+>!(result instanceof RegExp) : boolean
+>(result instanceof RegExp) : boolean
+>result instanceof RegExp : boolean
+>result : I
+>RegExp : RegExpConstructor
+
+    result = result2;
+>result = result2 : I
+>result : I
+>result2 : I
+
+} else if (!result.global) {
+>!result.global : boolean
+>result.global : string
+>result : I
+>global : string
+}
diff --git a/tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOf.ts b/tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOf.ts
new file mode 100644
index 0000000000..2750eb96eb
--- /dev/null
+++ b/tests/cases/conformance/expressions/typeGuards/typeGuardsWithInstanceOf.ts
@@ -0,0 +1,8 @@
+interface I { global: string; }
+var result: I;
+var result2: I;
+
+if (!(result instanceof RegExp)) {
+    result = result2;
+} else if (!result.global) {
+}
\ No newline at end of file