diff --git a/lib/BaseViewer.spec.ts b/lib/BaseViewer.spec.ts
index 7a2defa1d7..1e81ef30a6 100644
--- a/lib/BaseViewer.spec.ts
+++ b/lib/BaseViewer.spec.ts
@@ -8,7 +8,7 @@ import BaseViewer, {
   ImportParseStartEvent,
   SaveXMLDoneEvent,
   SaveXMLStartEvent
-} from './BaseViewer';
+} from './BaseViewer.js';
 
 import OverlaysModule from 'diagram-js/lib/features/overlays';
 import Canvas from 'diagram-js/lib/core/Canvas';