diff --git a/modules/update/update.test b/modules/update/update.test
index 0db9158..d174199 100644
--- a/modules/update/update.test
+++ b/modules/update/update.test
@@ -593,7 +593,9 @@ class UpdateTestUploadCase extends UpdateTestHelper {
    */
   public function testUploadModule() {
     // Images are not valid archives, so get one and try to install it.
-    $invalidArchiveFile = reset($this->drupalGetTestFiles('image'));
+    $imageTestFiles = $this->drupalGetTestFiles('image');
+    // $this->drupalGetTestFiles('image') has to be stored in a variable due to reset() requiring a reference
+    $invalidArchiveFile = reset($imageTestFiles);
     $edit = array(
       'files[project_upload]' => $invalidArchiveFile->uri,
     );