diff --git a/feeds.feeds.inc b/feeds.feeds.inc
index ba8c8f3..a51a7a6 100644
--- a/feeds.feeds.inc
+++ b/feeds.feeds.inc
@@ -55,16 +55,14 @@ function feeds_normalize_targets(array &$targets) {
  *   The target arary.
  */
 function _feeds_filter_callback_arrays(array &$target) {
-  static $normalize = array('summary_callback', 'form_callback');
-
   // Migrate keys summary_callback and form_callback to the new keys.
-  foreach ($normalize as $key) {
-    if (!empty($target[$key])) {
-      $target[$key . 's'][] = $target[$key];
-    }
-
-    unset($target[$key]);
+  if (isset($target['summary_callback'])) {
+    $target['summary_callbacks'][] = $target['summary_callback'];
+  }
+  if (isset($target['form_callback'])) {
+    $target['form_callbacks'][] = $target['form_callback'];
   }
+  unset($target['summary_callback'], $target['form_callback']);
 
   static $callback_keys = array(
     'summary_callbacks',
@@ -73,7 +71,7 @@ function _feeds_filter_callback_arrays(array &$target) {
     'unique_callbacks',
   );
 
-  // Filter out any incorect callbaks. Do it here so it only has to be done
+  // Filter out any incorrect callbacks. Do it here so it only has to be done
   // once.
   foreach ($callback_keys as $callback_key) {
     $target[$callback_key] = array_filter($target[$callback_key], 'is_callable');
diff --git a/feeds_ui/feeds_ui.admin.inc b/feeds_ui/feeds_ui.admin.inc
index 6a794b8..f975ffe 100644
--- a/feeds_ui/feeds_ui.admin.inc
+++ b/feeds_ui/feeds_ui.admin.inc
@@ -637,7 +637,7 @@ function feeds_ui_mapping_settings_form($form, $form_state, $i, $mapping, $targe
     $settings_form = array();
 
     foreach ($target['form_callbacks'] as $callback) {
-      $settings_form += $callback($mapping, $target, $form, $form_state);
+      $settings_form += call_user_func($callback, $mapping, $target, $form, $form_state);
     }
 
     // Merge in the optional unique form.
@@ -665,7 +665,7 @@ function feeds_ui_mapping_settings_form($form, $form_state, $i, $mapping, $targe
     $summary = array();
 
     foreach ($target['summary_callbacks'] as $callback) {
-      $summary[] = $callback($mapping, $target, $form, $form_state);
+      $summary[] = call_user_func($callback, $mapping, $target, $form, $form_state);
     }
 
     // Filter out empty summary values.
diff --git a/plugins/FeedsProcessor.inc b/plugins/FeedsProcessor.inc
index ebf532f..a332805 100644
--- a/plugins/FeedsProcessor.inc
+++ b/plugins/FeedsProcessor.inc
@@ -696,9 +696,7 @@ abstract class FeedsProcessor extends FeedsPlugin {
     $sources = $this->getCachedSources();
 
     if (isset($sources[$source_key]['callback'])) {
-      $callback = $sources[$source_key]['callback'];
-
-      return $callback($source, $result, $source_key);
+      return call_user_func($sources[$source_key]['callback'], $source, $result, $source_key);
     }
 
     return feeds_importer($this->id)->parser->getSourceElement($source, $result, $source_key);
@@ -721,7 +719,7 @@ abstract class FeedsProcessor extends FeedsPlugin {
 
     if (isset($targets[$target]['preprocess_callbacks'])) {
       foreach ($targets[$target]['preprocess_callbacks'] as $callback) {
-        $callback($source, $target_item, $target, $mapping);
+        call_user_func($callback, $source, $target_item, $target, $mapping);
       }
     }
 
@@ -730,14 +728,12 @@ abstract class FeedsProcessor extends FeedsPlugin {
     // setTargetElement().
     if (isset($targets[$target]['callback'])) {
 
-      $callback = $targets[$target]['callback'];
-
       // All target callbacks expect an array.
       if (!is_array($value)) {
         $value = array($value);
       }
 
-      $callback($source, $target_item, $target, $value, $mapping);
+      call_user_func($targets[$target]['callback'], $source, $target_item, $target, $value, $mapping);
     }
 
     else {
@@ -957,7 +953,7 @@ abstract class FeedsProcessor extends FeedsPlugin {
         }
 
         foreach ($targets[$target]['unique_callbacks'] as $callback) {
-          if ($entity_id = $callback($source, $this->entityType(), $this->bundle(), $target, $value)) {
+          if ($entity_id = call_user_func($callback, $source, $this->entityType(), $this->bundle(), $target, $value)) {
             // Stop at the first unique ID returned by a callback.
             break;
           }
diff --git a/tests/feeds_tests.module b/tests/feeds_tests.module
index 99f4df3..19eb2c2 100644
--- a/tests/feeds_tests.module
+++ b/tests/feeds_tests.module
@@ -130,7 +130,11 @@ function feeds_tests_feeds_processor_targets($entity_type, $bundle) {
     'callback' => 'feeds_tests_mapper_set_target',
     'optional_unique' => TRUE,
     'unique_callbacks' => array('feeds_tests_mapper_unique'),
-    'preprocess_callbacks' => array(array('FeedsTestsPreprocess', 'callback')),
+    'preprocess_callbacks' => array(
+      array('FeedsTestsPreprocess', 'callback'),
+      // Make sure that invalid callbacks are filtered.
+      '__feeds_tests_invalid_callback',
+    ),
   );
 
   return $targets;