diff --git a/scripts/run-tests.sh b/scripts/run-tests.sh
index 3266db3ad185..572bd6885ca0 100755
--- a/scripts/run-tests.sh
+++ b/scripts/run-tests.sh
@@ -162,7 +162,7 @@ function simpletest_script_parse_args() {
     'list' => FALSE,
     'clean' => FALSE,
     'url' => '',
-    'php' => NULL,
+    'php' => '',
     'concurrency' => 1,
     'all' => FALSE,
     'class' => FALSE,