diff --git a/lib/Doctrine/ODM/MongoDB/Mapping/ClassMetadata.php b/lib/Doctrine/ODM/MongoDB/Mapping/ClassMetadata.php
index <HASH>..<HASH> 100644
--- a/lib/Doctrine/ODM/MongoDB/Mapping/ClassMetadata.php
+++ b/lib/Doctrine/ODM/MongoDB/Mapping/ClassMetadata.php
@@ -898,6 +898,7 @@ class ClassMetadata
             'db',
             'collection',
             'rootDocumentName',
+            'allowCustomID',
         );
 
         if ($this->inheritanceType != self::INHERITANCE_TYPE_NONE) {
@@ -932,4 +933,4 @@ class ClassMetadata
             $this->reflFields[$field] = $reflField;
         }
     }
-}
\ No newline at end of file
+}
Fixed issue with allowCustomID being lost on serialization