diff --git a/packages/engine/Source/Core/addAll.js b/packages/engine/Source/Core/addAll.js
index 59401f0fd25..c2e0cfbc6d6 100644
--- a/packages/engine/Source/Core/addAll.js
+++ b/packages/engine/Source/Core/addAll.js
@@ -1,4 +1,4 @@
-import defined from "./defined";
+import defined from "./defined.js";
 
 /**
  * Adds all elements from the given source array to the given target array.