diff --git a/run-tests.php b/run-tests.php
index 1cc4592c2b4..43db6ca6c72 100755
--- a/run-tests.php
+++ b/run-tests.php
@@ -168,6 +168,11 @@ function initialize()
         dowriteln("available in the PATH environment variable.");
         exit;
     }
+    if ($windows_p) {
+	// modify path to help Windows find DLL files
+	$path = dirname($php) . ";" . getenv("PATH");
+	setenv("PATH={$path}");
+    }
 
     create_compiled_in_modules_list();