diff --git a/lib/mongo/types/undefined.rb b/lib/mongo/types/undefined.rb
index d883579..ac062fc 100644
--- a/lib/mongo/types/undefined.rb
+++ b/lib/mongo/types/undefined.rb
@@ -22,7 +22,7 @@ module Mongo
 
     def initialize
       super
-      warn "the Undefined type is deprecated and will be removed - BSON undefineds get implicitely converted to nil now"
+      warn "the Undefined type is deprecated and will be removed - BSON undefineds get implicitly converted to nil now"
     end
   end
 end