diff --git a/src/components/views/rooms/MessageComposerInput.js b/src/components/views/rooms/MessageComposerInput.js
index 63be026608..636addb79c 100644
--- a/src/components/views/rooms/MessageComposerInput.js
+++ b/src/components/views/rooms/MessageComposerInput.js
@@ -890,6 +890,7 @@ export default class MessageComposerInput extends React.Component {
             }
         } else {
             this.moveAutocompleteSelection(up);
+            e.preventDefault();
         }
     };