diff --git a/ChangeLog b/ChangeLog
index 725b679a1c..5d3ebaeaf5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Dec 31 15:44:48 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* lib/mkmf.rb (RbConfig): expand RUBY_SO_NAME for extensions
+	  backward compatibility.  [ruby-core:59426] [Bug #9329]
+
 Mon Dec 30 23:33:07 2013  Ayumu AIZAWA  <ayumu.aizawa@gmail.com>
 
 	* variable.c: [DOC] adding extra example in docs.
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 27345275a3..0c3b2cb513 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -2509,6 +2509,8 @@ MESSAGE
   $configure_args["--topdir"] ||= $curdir
   $ruby = arg_config("--ruby", File.join(RbConfig::CONFIG["bindir"], CONFIG["ruby_install_name"]))
 
+  RbConfig.expand(CONFIG["RUBY_SO_NAME"])
+
   # :startdoc:
 
   split = Shellwords.method(:shellwords).to_proc