diff --git a/src/StackMiddleware/BasicAuthMiddleware.php b/src/StackMiddleware/BasicAuthMiddleware.php
index d955dcd..e58f150 100644
--- a/src/StackMiddleware/BasicAuthMiddleware.php
+++ b/src/StackMiddleware/BasicAuthMiddleware.php
@@ -54,7 +54,7 @@ class BasicAuthMiddleware implements HttpKernelInterface {
    */
   public function handle(Request $request, $type = self::MASTER_REQUEST, $catch = TRUE) {
     $username = $request->headers->get('PHP_AUTH_USER');
-    if ($username) {
+    if ($username && !empty($_SERVER['PHP_AUTH_USER'])) {
       $pattern = $this->getPattern();
       // If username does not match pattern then do not authenticate that user.
       if (!preg_match($pattern, $_SERVER['PHP_AUTH_USER'])) {