diff --git a/ext/extmk.rb b/ext/extmk.rb
index 04d374ece6..dc6bd04945 100755
--- a/ext/extmk.rb
+++ b/ext/extmk.rb
@@ -106,7 +106,7 @@ def extract_makefile(makefile, keep = true)
   srcs = Dir[File.join($srcdir, "*.{#{SRC_EXT.join(%q{,})}}")].map {|fn| File.basename(fn)}.sort
   if !srcs.empty?
     old_srcs = m[/^ORIG_SRCS[ \t]*=[ \t](.*)/, 1] or return false
-    old_srcs.split.sort == srcs or return false
+    (old_srcs.split - srcs).empty? or return false
   end
   $target = target
   $extconf_h = m[/^RUBY_EXTCONF_H[ \t]*=[ \t]*(\S+)/, 1]