diff --git a/modules/image/image.module b/modules/image/image.module
index 07f4892..2c07fcc 100644
--- a/modules/image/image.module
+++ b/modules/image/image.module
@@ -786,7 +786,19 @@ function image_style_deliver($style, $scheme) {
       file_download($scheme, file_uri_target($derivative_uri));
     }
     else {
-      $headers = module_invoke_all('file_download', $image_uri);
+      $headers = array();
+      foreach (module_implements('file_download') as $module) {
+        $function = $module . '_file_download';
+        $result = $function($image_uri);
+        if ($result == -1) {
+          // Throw away the headers received so far.
+          $headers = array();
+          break;
+        }
+        if (isset($result) && is_array($result)) {
+          $headers = array_merge($headers, $result);
+        }
+      }
       if (in_array(-1, $headers) || empty($headers)) {
         return drupal_access_denied();
       }