diff --git a/src/vs/workbench/workbench.web.api.ts b/src/vs/workbench/workbench.web.api.ts
index 16b5f29dd36..640931217ca 100644
--- a/src/vs/workbench/workbench.web.api.ts
+++ b/src/vs/workbench/workbench.web.api.ts
@@ -247,7 +247,7 @@ interface ISettingsSyncOptions {
 	/**
 	 * Handler is being called when the user changes Settings Sync enablement.
 	 */
-	enablementHandler(enablement: boolean): void;
+	enablementHandler?(enablement: boolean): void;
 }
 
 interface IWorkbenchConstructionOptions {