diff --git a/app/javascript/mastodon/features/ui/index.js b/app/javascript/mastodon/features/ui/index.js
index f1409b946..3c1a266e3 100644
--- a/app/javascript/mastodon/features/ui/index.js
+++ b/app/javascript/mastodon/features/ui/index.js
@@ -230,7 +230,7 @@ export default class UI extends React.PureComponent {
       this.dragTargets.push(e.target);
     }
 
-    if (e.dataTransfer && e.dataTransfer.types.includes('Files')) {
+    if (e.dataTransfer && Array.from(e.dataTransfer.types).includes('Files')) {
       this.setState({ draggingOver: true });
     }
   }