diff --git a/ext/etc/extconf.rb b/ext/etc/extconf.rb
index 20a7dd00d6..435fbe7f3d 100644
--- a/ext/etc/extconf.rb
+++ b/ext/etc/extconf.rb
@@ -41,6 +41,12 @@ have_struct_member('struct passwd', 'pw_expire', 'pwd.h')
 have_struct_member('struct passwd', 'pw_passwd', 'pwd.h')
 have_struct_member('struct group', 'gr_passwd', 'grp.h')
 
+# for https://github.com/ruby/etc
+srcdir = File.expand_path("..", __FILE__)
+if !File.exist?("#{srcdir}/depend")
+  %x[#{RbConfig.ruby} #{srcdir}/mkconstants.rb -o #{srcdir}/constdefs.h]
+end
+
 $distcleanfiles << "constdefs.h"
 
 create_makefile("etc")