--- a/testing/mochitest/tests/SimpleTest/SimpleTest.js
+++ b/testing/mochitest/tests/SimpleTest/SimpleTest.js
@@ -782,17 +782,17 @@ SimpleTest.waitForFocus = function (call
           } else {
               childDesiredWindow = SpecialPowers.getFocusedElementForWindow(desiredWindow, true);
           }
 
           /* If this is a child frame, ensure that the frame is focused. */
           focused = (focusedWindow() == childDesiredWindow);
           if (!focused) {
               info("must wait for focus");
-              desiredWindow.addEventListener("focus", focusedOrLoaded, true);
+              childDesiredWindow.addEventListener("focus", focusedOrLoaded, true);
               if (isChildProcess) {
                   childDesiredWindow.focus();
               }
               else {
                   SpecialPowers.focus(childDesiredWindow);
               }
           }