diff -u -wr a/tool/mkconfig.rb b/tool/mkconfig.rb
--- a/tool/mkconfig.rb  2012-10-08 05:57:16.948702976 +0200
+++ b/tool/mkconfig.rb  2011-08-13 15:17:30.000000000 +0200
@@ -40,6 +40,7 @@
 v_fast = []
 v_others = []
 vars = {}
+v_runtime = {}
 continued_name = nil
 continued_line = nil
 File.foreach "config.status" do |line|
@@ -118,7 +119,10 @@
     val = val.gsub(/\$(?:\$|\{?(\w+)\}?)/) {$1 ? "$(#{$1})" : $&}.dump
     case name
     when /^prefix$/
+      v_runtime[:prefix] = val.slice(1..-2)
       val = "(TOPDIR || DESTDIR + #{val})"
+    when /^libdir$/
+      v_runtime[:libdir] = File.basename(val.slice(1..-2))
     when /^ARCH_FLAG$/
       val = "arch_flag || #{val}" if universal
     when /^UNIVERSAL_ARCHNAMES$/
@@ -145,7 +149,7 @@

 drive = File::PATH_SEPARATOR == ';'

-prefix = "/lib/ruby/#{version}/#{arch}"
+prefix = "/#{v_runtime[:libdir]}/ruby/#{version}/#{arch}"
 print "  TOPDIR = File.dirname(__FILE__).chomp!(#{prefix.dump})\n"
 print "  DESTDIR = ", (drive ? "TOPDIR && TOPDIR[/\\A[a-z]:/i] || " : ""), "'' unless defined? DESTDIR\n"
 print <<'ARCH' if universal
@@ -190,6 +194,7 @@
     x
   end
 end
+v_others.map!{|x| x.gsub(v_runtime[:prefix], "$(prefix)") }
 v_others.compact!

 if $install_name