diff --git a/src/vs/workbench/parts/debug/common/debugProtocol.d.ts b/src/vs/workbench/parts/debug/common/debugProtocol.d.ts
index 89f466c1209d783f871cd4ca3e425ffa118419a4..3391d27b9b1ba751fee10b5e75c914bead728c4d 100644
--- a/src/vs/workbench/parts/debug/common/debugProtocol.d.ts
+++ b/src/vs/workbench/parts/debug/common/debugProtocol.d.ts
@@ -179,7 +179,7 @@ declare module DebugProtocol {
 		pathFormat?: string;
 
 		/** Client supports the optional type attribute for variables. */
-		supportsVariableType: boolean;
+		supportsVariableType?: boolean;
 	}
 	/** Response to Initialize request. */
 	export interface InitializeResponse extends Response {