diff --git a/ChangeLog b/ChangeLog
index 9804f7ab5b..24dcb1134e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Dec 10 05:53:18 2015  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* tool/mkconfig.rb: rbconfig must not be fronzen-string-literal to
+	  expand CONFIG hash.  [ruby-core:72006] [Bug #11798]
+
 Thu Dec 10 05:03:51 2015  Eric Wong  <e@80x24.org>
 
 	* ext/socket/ifaddr.c (ifaddr_mark): remove empty function
diff --git a/tool/mkconfig.rb b/tool/mkconfig.rb
index 49b841f775..fdba7097d6 100755
--- a/tool/mkconfig.rb
+++ b/tool/mkconfig.rb
@@ -172,6 +172,7 @@ prefix = vars.expand(vars["prefix"] ||= "")
 rubyarchdir = vars.expand(vars["rubyarchdir"] ||= "")
 relative_archdir = rubyarchdir.rindex(prefix, 0) ? rubyarchdir[prefix.size..-1] : rubyarchdir
 puts %[\
+# frozen-string-literal: false
 # This file was created by #{mkconfig} when ruby was built.  It contains
 # build information for ruby which is used e.g. by mkmf to build
 # compatible native extensions.  Any changes made to this file will be