diff --git a/src/php/tests/interop/interop_client.php b/src/php/tests/interop/interop_client.php
index 3e19c7ae339..19cbf21bc2b 100755
--- a/src/php/tests/interop/interop_client.php
+++ b/src/php/tests/interop/interop_client.php
@@ -530,7 +530,7 @@ function _makeStub($args)
         throw new Exception('Missing argument: --test_case is required');
     }
 
-    if ($args['server_port'] === 443) {
+    if ($args['server_port'] === '443') {
         $server_address = $args['server_host'];
     } else {
         $server_address = $args['server_host'].':'.$args['server_port'];