diff --git a/testing/web-platform/tests/tools/wptrunner/wptrunner/executors/executorservo.py b/testing/web-platform/tests/tools/wptrunner/wptrunner/executors/executorservo.py
index 6988f2d69fa39..7d8bf03bad2f5 100644
--- a/testing/web-platform/tests/tools/wptrunner/wptrunner/executors/executorservo.py
+++ b/testing/web-platform/tests/tools/wptrunner/wptrunner/executors/executorservo.py
@@ -334,6 +334,8 @@ def do_test(self, test):
         self.test = test
         success, data = ServoTimedRunner(self.logger, self.do_crashtest, self.protocol,
                                          test_url, timeout, self.extra_timeout).run()
+        # Ensure that no processes hang around if they timeout.
+        self.proc.kill()
 
         if success:
             return self.convert_result(test, data)