diff --git a/tests/Composer/TestCase.php b/tests/Composer/TestCase.php
index a065f200c..299ac9903 100644
--- a/tests/Composer/TestCase.php
+++ b/tests/Composer/TestCase.php
@@ -63,7 +63,7 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
 
         do {
             $unique = $root . DIRECTORY_SEPARATOR . uniqid('composer-test-');
-            if (!file_exists($unique) && mkdir($unique, 0777)) {
+            if (!file_exists($unique) && false !== @mkdir($unique, 0777)) {
                 return realpath($unique);
             }
         } while (--$attempts);