diff --git a/tools/run_tests/run_interop_tests.py b/tools/run_tests/run_interop_tests.py
index 1814ba1abc3be2f45ce4ed69f8881948b1bd3dec..c9e2f09b2d25f51692272b95ccddbea90355075a 100755
--- a/tools/run_tests/run_interop_tests.py
+++ b/tools/run_tests/run_interop_tests.py
@@ -220,11 +220,11 @@ class PHPLanguage:
 
   def cloud_to_prod_args(self):
     return (self.client_cmdline_base + _CLOUD_TO_PROD_BASE_ARGS +
-            ['--use_tls'])
+            ['--use_tls=true'])
 
   def cloud_to_cloud_args(self):
     return (self.client_cmdline_base + _CLOUD_TO_CLOUD_BASE_ARGS +
-            ['--use_tls', '--use_test_ca'])
+            ['--use_tls=true', '--use_test_ca=true'])
 
   def cloud_to_prod_env(self):
     return _SSL_CERT_ENV