diff --git a/core/connection_previewers/insertion_marker_previewer.ts b/core/connection_previewers/insertion_marker_previewer.ts
index 574fa8409..3f6f15841 100644
--- a/core/connection_previewers/insertion_marker_previewer.ts
+++ b/core/connection_previewers/insertion_marker_previewer.ts
@@ -196,6 +196,7 @@ export class InsertionMarkerPreviewer implements IConnectionPreviewer {
   ) {
     const origConns = orig.getConnections_(true);
     const markerConns = marker.getConnections_(true);
+    if (origConns.length !== markerConns.length) return null;
     for (let i = 0; i < origConns.length; i++) {
       if (origConns[i] === origConn) {
         return markerConns[i];