diff --git a/ChangeLog b/ChangeLog
index 4388dd26a2..84052a816b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Aug 23 11:07:08 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* win32/Makefile.sub (config.h): now SIZEOF_CLOCK_T is needed for
+	  unsigned_clock_t.
+
 Thu Aug 22 22:01:04 2013  Tanaka Akira  <akr@fsij.org>
 
 	* process.c (rb_clock_gettime): Strip "s" from unit names.
diff --git a/win32/Makefile.sub b/win32/Makefile.sub
index cf0c743b8e..7d615b643c 100644
--- a/win32/Makefile.sub
+++ b/win32/Makefile.sub
@@ -538,6 +538,7 @@ $(CONFIG_H): $(MKFILES) $(srcdir)/win32/Makefile.sub $(win_srcdir)/Makefile.sub
 !endif
 #define CLOCKID2NUM(v) INT2NUM(v)
 #define NUM2CLOCKID(v) NUM2INT(v)
+#define SIZEOF_CLOCK_T 4
 #define SIZEOF_RLIM_T 0
 !if "$(ARCH)" == "x64" || "$(ARCH)" == "ia64"
 #define SIZEOF_SIZE_T 8