diff --git a/tests/feeds_tests.module b/tests/feeds_tests.module
index 8d3a1db..99f4df3 100644
--- a/tests/feeds_tests.module
+++ b/tests/feeds_tests.module
@@ -121,7 +121,7 @@ function feeds_tests_feeds_processor_targets($entity_type, $bundle) {
     'callback' => 'feeds_tests_mapper_set_target',
     'summary_callbacks' => array('feeds_tests_mapper_summary'),
     'form_callbacks' => array('feeds_tests_mapper_form'),
-    'preprocess_callbacks' => array('feeds_tests_preprocess_callback'),
+    'preprocess_callbacks' => array(array(new FeedsTestsPreprocess(), 'callback')),
   );
 
   $targets['test_unique_target'] = array(
@@ -130,7 +130,7 @@ function feeds_tests_feeds_processor_targets($entity_type, $bundle) {
     'callback' => 'feeds_tests_mapper_set_target',
     'optional_unique' => TRUE,
     'unique_callbacks' => array('feeds_tests_mapper_unique'),
-    'preprocess_callbacks' => array('feeds_tests_preprocess_callback'),
+    'preprocess_callbacks' => array(array('FeedsTestsPreprocess', 'callback')),
   );
 
   return $targets;
@@ -269,3 +269,19 @@ function feeds_tests_mapper_unique(FeedsSource $source, $entity_type, $bundle, $
     return key($result[$entity_type]);
   }
 }
+
+/**
+ * Helper class to ensure callbacks can be objects.
+ */
+class FeedsTestsPreprocess {
+
+/**
+ * Preprocess callback for test_target.
+ *
+ * @see feeds_tests_feeds_processor_targets()
+ */
+  public static function callback(FeedsSource $source, $target_item, $target, array &$mapping) {
+    $mapping['required_value'] = TRUE;
+  }
+
+}