diff -ru a/libmolsketch/molscene.cpp b/libmolsketch/molscene.cpp
--- a/libmolsketch/molscene.cpp	2019-03-13 20:46:48.000000000 +0000
+++ b/libmolsketch/molscene.cpp	2020-05-04 10:20:23.256668324 +0100
@@ -618,7 +618,7 @@
   void MolScene::dragEnterEvent(QGraphicsSceneDragDropEvent *event)
   {
     if (!event->mimeData() || !event->mimeData()->hasFormat(mimeType())) return;
-    if (!event->proposedAction() == Qt::CopyAction) return;
+    if ((!event->proposedAction()) == Qt::CopyAction) return;
     event->accept();
     for (genericAction* action : sceneActions())
       action->setChecked(false);