diff --git a/tools/build/_/index.ts b/tools/build/_/index.ts
index 82b7dcdf7..7965fad62 100644
--- a/tools/build/_/index.ts
+++ b/tools/build/_/index.ts
@@ -137,7 +137,7 @@ export function watch(
 ): Observable<string> {
   return fromEvent(
     chokidar.watch(pattern, options),
-    "change"
+    "change", file => file
   ) as Observable<string>
 }