diff --git a/test/mouse.spec.js b/test/mouse.spec.js
index 3e8c7551d9..28256de345 100644
--- a/test/mouse.spec.js
+++ b/test/mouse.spec.js
@@ -156,7 +156,7 @@ module.exports.describe = function({testRunner, expect, FFOX, CHROMIUM, WEBKIT,
         await page.mouse.down();
         await page.hover('#target');
         await page.mouse.up();
-        expect(await page.$eval('#target', target => target.contains(document.querySelector('#source')))).toBe(true);
+        expect(await page.$eval('#target', target => target.contains(document.querySelector('#source')))).toBe(true, 'could not find source in target');
       })
     });
   });