diff --git a/src/WindowBehavior.ts b/src/WindowBehavior.ts
index f85c6b6..44ae5c4 100644
--- a/src/WindowBehavior.ts
+++ b/src/WindowBehavior.ts
@@ -16,7 +16,7 @@ const handleResize = (canvas: HTMLCanvasElement) => {
   }
 };
 
-const saveBeforeExit = (app: Editor): void => {
+const saveBeforeExit = (app: Editor): null => {
   // @ts-ignore
   event.preventDefault();
   // Iterate over all local files and set the candidate to the committed