diff --git a/ui/core.js b/ui/core.js
index eaf11d0a82b..a8167d68318 100644
--- a/ui/core.js
+++ b/ui/core.js
@@ -63,6 +63,13 @@ $.extend( $.ui, {
 			activeElement = document.body;
 		}
 
+		// Support: IE 11 only
+		// IE11 returns a seemingly empty object in some cases when accessing
+		// document.activeElement from an <iframe>
+		if ( !activeElement.nodeName ) {
+			activeElement = document.body;
+		}
+
 		return activeElement;
 	},