diff --git a/web/editor.js b/web/editor.js
index b74035de6..4525537ba 100644
--- a/web/editor.js
+++ b/web/editor.js
@@ -162,6 +162,9 @@ function focusPrevious() {
 }
 
 function onDragOver(elem) {
+    var e = window.event;
+    e.dataTransfer.dropEffect = "copy";
+    e.preventDefault();
     // if we focus the target element immediately, the drag&drop turns into a
     // copy, so note it down for later instead
     dropTarget = elem;