diff --git a/lib/mongo/util/ordered_hash.rb b/lib/mongo/util/ordered_hash.rb
index faaf4b7..ce459ba 100644
--- a/lib/mongo/util/ordered_hash.rb
+++ b/lib/mongo/util/ordered_hash.rb
@@ -64,7 +64,7 @@ class OrderedHash < Hash
   end
 
   def delete(key, &block)
-    @ordered_keys.delete(key)
+    @ordered_keys.delete(key) if @ordered_keys
     super
   end