diff --git a/tools/run_tests/run_interop_tests.py b/tools/run_tests/run_interop_tests.py
index 1a83c10a42c..2d7f4a625d6 100755
--- a/tools/run_tests/run_interop_tests.py
+++ b/tools/run_tests/run_interop_tests.py
@@ -728,8 +728,7 @@ def server_jobspec(language, docker_image, insecure=False, manual_cmd_log=None):
     ]
 
   else:
-    portstr = str(_DEFAULT_SERVER_PORT)
-    docker_args += ['-p', '%s:%s'%(portstr, portstr)]
+    docker_args += ['-p', str(_DEFAULT_SERVER_PORT)]
 
   docker_cmdline = docker_run_cmdline(cmdline,
                                       image=docker_image,