diff --git a/feeds_tamper.module b/feeds_tamper.module
index e390264..12d2e63 100644
--- a/feeds_tamper.module
+++ b/feeds_tamper.module
@@ -19,16 +19,20 @@ function feeds_tamper_feeds_after_parse(FeedsSource $source, &$result) {
     foreach ($importer_instances as $element_key => $instances) {
       foreach ($instances as $instance) {
         $plugin = feeds_tamper_get_plugin($instance->plugin_id);
+        // Ensure our plugin is defining a valid callback.
+        if (!(isset($plugin['callback']) && function_exists($plugin['callback']))) {
+          continue;
+        }
         if (is_array($item[$element_key]) && $plugin['multi'] == 'loop') {
           foreach ($item[$element_key] as &$i) {
             $plugin['callback']($source, $item_key, $element_key, $i, $instance->settings);
           }
         }
-  
+
         else if (is_array($item[$element_key]) && $plugin['multi'] == 'direct') {
           $plugin['callback']($source, $item_key, $element_key, $item[$element_key], $instance->settings);
         }
-  
+
         else if (!is_array($item[$element_key]) && $plugin['single'] != 'skip') {
           $plugin['callback']($source, $item_key, $element_key, $item[$element_key], $instance->settings);
         }
@@ -171,4 +175,4 @@ function feeds_tamper_ctools_plugin_type() {
 
 function feeds_tamper_make_machine($string) {
   return substr(preg_replace('/[^a-z0-9-]/', '_', strtolower($string)), 0, 127);
-}
\ No newline at end of file
+}