diff --git a/ChangeLog b/ChangeLog
index 22b7417680..5971645238 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Dec 22 17:39:03 2007  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* lib/mkmf.rb ($extmk): fixed broken condition.
+
 Sat Dec 22 17:35:59 2007  NARUSE, Yui <naruse@ruby-lang.org>
 
 	* ext/nkf/nkf-utf8.c: Update nkf.c rev:1.157.
@@ -7,10 +11,6 @@ Sat Dec 22 17:35:59 2007  NARUSE, Yui <naruse@ruby-lang.org>
 	* ext/nkf/kconv.c (Kconv#kconv, to*): use self.encoding as from_enc
 	  when from_enc isn't given.
 
-Sat Dec 22 17:31:41 2007  NAKAMURA Usaku  <usa@ruby-lang.org>
-
-	* lib/mkmf.rb ($extmk): fixed broken condition.
-
 Sat Dec 22 17:06:50 2007  GOTOU Yuuzou  <gotoyuzo@notwork.org>
 
 	* ext/openssl/lib/net/ssl.rb (OpenSSL::SSL::SSLContext.build): removed.
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 7cd62e5053..d93826cce3 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -146,7 +146,7 @@ end
 topdir = File.dirname(libdir = File.dirname(__FILE__))
 extdir = File.expand_path("ext", topdir)
 path = File.expand_path($0)
-$extmk = path[0, topdir.size+1] == topdir+"/" && %r"(ext|enc|tool)/" =~ path[topdir.size+1..-1]
+$extmk = path[0, topdir.size+1] == topdir+"/" && %r"\A(ext|enc|tool)\z" =~ File.dirname(path[topdir.size+1..-1])
 if not $extmk and File.exist?(($hdrdir = RbConfig::CONFIG["rubyhdrdir"]) + "/ruby/ruby.h")
   $topdir = $hdrdir
   $top_srcdir = $hdrdir