diff --git a/ChangeLog b/ChangeLog
index 388d7c7f8c..15e83f5e75 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Dec  6 09:14:38 2010  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* lib/mkmf.rb (check_signedness): rename unused variable prelude.
+
 Sun Dec  5 17:56:36 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* class.c (make_metaclass): fix probable typo.  builtin type flag
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 71647b1816..02e0b4bc2b 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -1143,7 +1143,7 @@ end
 # done.
 #
 def check_signedness(type, headers = nil, opts = nil, &b)
-  typedef, member, prelude = typedef_expr(type, headers)
+  typedef, member, _ = typedef_expr(type, headers)
   signed = nil
   checking_for("signedness of #{type}", STRING_OR_FAILED_FORMAT) do
     signed = try_signedness(typedef, member, headers, opts, &b) or next nil