diff --git a/src/compiler/core.ts b/src/compiler/core.ts
index 8b654c16b9c..f344fa08704 100644
--- a/src/compiler/core.ts
+++ b/src/compiler/core.ts
@@ -203,6 +203,8 @@ namespace ts {
      * Filters an array by a predicate function. Returns the same array instance if the predicate is
      * true for all elements, otherwise returns a new array instance containing the filtered subset.
      */
+    export function filter<T, U extends T>(array: T[], f: (x: T) => x is U): U[];
+    export function filter<T>(array: T[], f: (x: T) => boolean): T[]
     export function filter<T>(array: T[], f: (x: T) => boolean): T[] {
         if (array) {
             const len = array.length;
diff --git a/src/compiler/transformers/ts.ts b/src/compiler/transformers/ts.ts
index efb247ba663..191966aa779 100644
--- a/src/compiler/transformers/ts.ts
+++ b/src/compiler/transformers/ts.ts
@@ -1034,7 +1034,7 @@ namespace ts {
          * @param isStatic A value indicating whether to get properties from the static or instance side of the class.
          */
         function getInitializedProperties(node: ClassExpression | ClassDeclaration, isStatic: boolean): PropertyDeclaration[] {
-            return filter(node.members, isStatic ? isStaticInitializedProperty : isInstanceInitializedProperty);
+            return filter(node.members, isStatic ? isStaticInitializedProperty : isInstanceInitializedProperty); 
         }
 
         /**