--- a/gfx/layers/apz/test/mochitest/apz_test_utils.js
+++ b/gfx/layers/apz/test/mochitest/apz_test_utils.js
@@ -268,16 +268,18 @@ function runSubtestsSeriallyInFreshWindo
           w = spawnTest(test.file);
         });
       } else {
         w = spawnTest(test.file);
       }
     }
 
     advanceSubtestExecution();
+  }).catch(function(e) {
+    SimpleTest.ok(false, "Error occurred while running subtests: " + e);
   });
 }
 
 function pushPrefs(prefs) {
   return SpecialPowers.pushPrefEnv({'set': prefs});
 }
 
 async function waitUntilApzStable() {