diff --git a/node-gcm/node-gcm.d.ts b/node-gcm/node-gcm.d.ts
index 21980416e..82b3d1957 100644
--- a/node-gcm/node-gcm.d.ts
+++ b/node-gcm/node-gcm.d.ts
@@ -39,8 +39,8 @@ declare module "node-gcm" {
 
         addData(key: string, value: string): void;
         addData(data: { [key: string]: string }): void;
-        addNotification(value: INotificationOptions);
-        addNotification(key: string, value:INotificationOptions);
+        addNotification(value: INotificationOptions): void;
+        addNotification(key: string, value:INotificationOptions): void;
     }