diff --git a/src/services/getScriptLexicalStructureWalker.ts b/src/services/getScriptLexicalStructureWalker.ts
index 1de84435cbf..94ed8a6de87 100644
--- a/src/services/getScriptLexicalStructureWalker.ts
+++ b/src/services/getScriptLexicalStructureWalker.ts
@@ -151,7 +151,7 @@ module TypeScript.Services {
             }
         }
 
-        private getNavigationBarItem(text: string, kind: string, kindModifiers: string, spans: TypeScript.TextSpan[], childItems?: ts.NavigationBarItem[], indent: number = 0): ts.NavigationBarItem {
+        private getNavigationBarItem(text: string, kind: string, kindModifiers: string, spans: TypeScript.TextSpan[], childItems: ts.NavigationBarItem[]= [], indent: number = 0): ts.NavigationBarItem {
             return {
                 text: text,
                 kind: kind,