diff --git a/types/polymer/index.d.ts b/types/polymer/index.d.ts
index b1f76d83c6..eee6a6250f 100644
--- a/types/polymer/index.d.ts
+++ b/types/polymer/index.d.ts
@@ -53,7 +53,7 @@ declare global {
 
       // Debouncer
 
-      debounce?(jobName: string, callback: Function, wait: number): void;
+      debounce?(jobName: string, callback: Function, wait?: number): void;
 
       isDebouncerActive?(jobName: string): boolean;