diff --git a/plugins/FeedsProcessor.inc b/plugins/FeedsProcessor.inc
index a332805..0ab04a0 100644
--- a/plugins/FeedsProcessor.inc
+++ b/plugins/FeedsProcessor.inc
@@ -719,7 +719,7 @@ abstract class FeedsProcessor extends FeedsPlugin {
 
     if (isset($targets[$target]['preprocess_callbacks'])) {
       foreach ($targets[$target]['preprocess_callbacks'] as $callback) {
-        call_user_func($callback, $source, $target_item, $target, $mapping);
+        call_user_func_array($callback, array($source, $target_item, $target, &$mapping));
       }
     }