diff --git a/neutron/tests/functional/test_server.py b/neutron/tests/functional/test_server.py
index b0a28c05efe..8bae960e883 100644
--- a/neutron/tests/functional/test_server.py
+++ b/neutron/tests/functional/test_server.py
@@ -213,7 +213,7 @@ class TestWsgiServer(TestNeutronServer):
 
             # Memorize a port that was chosen for the service
             self.port = server.port
-            os.write(self.pipeout, str(self.port))
+            os.write(self.pipeout, bytes(self.port))
 
             server.wait()