diff --git a/ChangeLog b/ChangeLog
index d908e2153d..00e838d9c6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Wed Jun 26 16:42:11 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/mkmf.rb: should use expanded values for header directories
+	  unless extmk.  patch by vo.x (Vit Ondruch) at [ruby-core:55653]
+	  [Bug #8115], rhbz#921650.
+
 Wed Jun 26 12:48:22 2013  Tanaka Akira  <akr@fsij.org>
 
 	* bignum.c (bigxor_int): Fix a buffer over read.
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 48562aafe0..146225d4d5 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -235,11 +235,10 @@ module MakeMakefile
     path = dir
   end
   $extmk ||= false
-  if not $extmk and File.exist?(RbConfig::CONFIG["rubyhdrdir"] + "/ruby/ruby.h")
-    $hdrdir = CONFIG["rubyhdrdir"]
+  if not $extmk and File.exist?(($hdrdir = RbConfig::CONFIG["rubyhdrdir"]) + "/ruby/ruby.h")
     $topdir = $hdrdir
     $top_srcdir = $hdrdir
-    $arch_hdrdir = CONFIG["rubyarchhdrdir"]
+    $arch_hdrdir = RbConfig::CONFIG["rubyarchhdrdir"]
   elsif File.exist?(($hdrdir = ($top_srcdir ||= topdir) + "/include")  + "/ruby.h")
     $topdir ||= RbConfig::CONFIG["topdir"]
     $arch_hdrdir = "$(extout)/include/$(arch)"