diff --git a/tests/wpt/web-platform-tests/tools/wptrunner/wptrunner/browsers/servodriver.py b/tests/wpt/web-platform-tests/tools/wptrunner/wptrunner/browsers/servodriver.py
index 74874fd6d2d..fe392e06651 100644
--- a/tests/wpt/web-platform-tests/tools/wptrunner/wptrunner/browsers/servodriver.py
+++ b/tests/wpt/web-platform-tests/tools/wptrunner/wptrunner/browsers/servodriver.py
@@ -99,6 +99,7 @@ class ServoWebDriverBrowser(Browser):
             str(port)
             for _protocol, ports in self.server_ports.items()
             for port in ports
+            if port
         )
 
         debug_args, command = browser_command(