diff --git a/ChangeLog b/ChangeLog
index 375cc29c6d..e69e53921b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Nov  2 04:41:33 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/mkmf.rb (MakeMakefile#timestamp_file): use ! instead of %, a GNU
+	  make special character.
+
 Fri Nov  2 04:40:10 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* test/ruby/test_process.rb (test_execopts_preserve_env_on_exec_failure):
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 62b3c5f3f6..84d736dac0 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -1859,7 +1859,7 @@ preload = #{defined?($preload) && $preload ? $preload.join(' ') : ''}
   end
 
   def timestamp_file(name)
-    name = name.gsub(/(\$[({]|[})])|(\/+)|[^-.\w]+/) {$1 ? "@" : $2 ? "%" : "_"}
+    name = name.gsub(/(\$[({]|[})])|(\/+)|[^-.\w]+/) {$1 ? "@" : $2 ? "!" : "_"}
     "./.#{name}.time"
   end
   # :startdoc: