diff --git a/tool/mkconfig.rb b/tool/mkconfig.rb
index c4f9d5bf2f..fbe4893a06 100755
--- a/tool/mkconfig.rb
+++ b/tool/mkconfig.rb
@@ -121,7 +121,7 @@ File.foreach "config.status" do |line|
       universal, val = val, 'universal' if universal
     when /^arch$/
       if universal
-        val.sub!(/universal/, %q[#{arch && universal[/(?:\A|\s)#{Regexp.quote(arch)}=(\S+)/, 1] || '\&'}])
+        val.sub!(/universal/, %q[#{arch && universal[/(?:\A|\s)#{Regexp.quote(arch)}=(\S+)/, 1] || RUBY_PLATFORM[/\A[^-]*/]}])
       end
     when /^oldincludedir$/
       val = '"$(SDKROOT)"'+val if /darwin/ =~ arch