diff --git a/packages/office-ui-fabric-react/src/components/ContextualMenu/ContextualMenu.tsx b/packages/office-ui-fabric-react/src/components/ContextualMenu/ContextualMenu.tsx
index b903ec04d74d5..14d89514d2594 100644
--- a/packages/office-ui-fabric-react/src/components/ContextualMenu/ContextualMenu.tsx
+++ b/packages/office-ui-fabric-react/src/components/ContextualMenu/ContextualMenu.tsx
@@ -459,6 +459,7 @@ export class ContextualMenu extends BaseComponent<IContextualMenuProps, IContext
 
     if (ev.which === openKey) {
       this._onItemSubMenuExpand(item, ev.currentTarget as HTMLElement);
+      ev.preventDefault();
     }
   }