diff --git a/ChangeLog b/ChangeLog
index 585976b8f7..be28a5c784 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Tue Jul  1 21:09:58 2008  URABE Shyouhei  <shyouhei@ruby-lang.org>
+
+	* lib/mkmf.rb (create_tmpsrc): we need to include COMMON_HEADERS,
+	  namely inclusion of ruby.h, because _GNU_SOURCE is now defined
+	  there (if any) and socket.so requires it on Linux systems.
+
 Tue Jul  1 20:55:07 2008  URABE Shyouhei  <shyouhei@ruby-lang.org>
 
 	* eval.c (rb_interrupt): trick to suppress GCC warning.
diff --git a/lib/mkmf.rb b/lib/mkmf.rb
index 74a20609b2..034ca0bf9c 100644
--- a/lib/mkmf.rb
+++ b/lib/mkmf.rb
@@ -321,6 +321,7 @@ end
 
 def create_tmpsrc(src)
   src = yield(src) if block_given?
+  src[0, 0] = COMMON_HEADERS + "\n"
   src = src.gsub(/[ \t]+$/, '').gsub(/\A\n+|^\n+$/, '').sub(/[^\n]\z/, "\\&\n")
   count = 0
   begin
@@ -1843,7 +1844,7 @@ split = Shellwords.method(:shellwords).to_proc
 
 EXPORT_PREFIX = config_string('EXPORT_PREFIX') {|s| s.strip}
 
-hdr = []
+hdr = ['#include "ruby.h"' "\n"]
 config_string('COMMON_MACROS') do |s|
   Shellwords.shellwords(s).each do |w|
     hdr << "#define " + w.split(/=/, 2).join(" ")