--- a/browser/components/sessionstore/test/browser_394759_purge.js
+++ b/browser/components/sessionstore/test/browser_394759_purge.js
@@ -88,18 +88,20 @@ add_task(function* () {
       }
     ]
   };
 
   // set browser to test state
   ss.setBrowserState(JSON.stringify(testState));
 
   // purge domain & check that we purged correctly for closed windows
+  let clearHistoryPromise = promiseClearHistory();
   yield ForgetAboutSite.removeDataFromDomain("mozilla.org");
-  yield promiseClearHistory();
+  yield clearHistoryPromise;
+
   let closedWindowData = JSON.parse(ss.getClosedWindowData());
 
   // First set of tests for _closedWindows[0] - tests basics
   let win = closedWindowData[0];
   is(win.tabs.length, 1, "1 tab was removed");
   is(countOpenTabsByTitle(win.tabs, FORGET), 0,
      "The correct tab was removed");
   is(countOpenTabsByTitle(win.tabs, REMEMBER), 1,