diff --git a/ChangeLog b/ChangeLog
index 596e7b3f95..78c7754a50 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Dec 11 11:11:03 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* include/ruby/st.h (size_t): needs stddef.h or stdlib.h.
+	  [ruby-core:20339]
+
 Thu Dec 11 10:25:25 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* test/ruby/test_bignum.rb (TestBignum#test_convert): remove
diff --git a/include/ruby/st.h b/include/ruby/st.h
index 84ef72b440..31bac7b1ad 100644
--- a/include/ruby/st.h
+++ b/include/ruby/st.h
@@ -12,6 +12,19 @@ extern "C" {
 #endif
 #endif
 
+#ifndef RUBY_LIB
+#include "ruby/config.h"
+#ifdef RUBY_EXTCONF_H
+#include RUBY_EXTCONF_H
+#endif
+#endif
+
+#if   defined STDC_HEADERS
+#include <stddef.h>
+#elif defined HAVE_STDLIB_H
+#include <stdlib.h>
+#endif
+
 #if SIZEOF_LONG == SIZEOF_VOIDP
 typedef unsigned long st_data_t;
 #elif SIZEOF_LONG_LONG == SIZEOF_VOIDP