diff --git a/ChangeLog b/ChangeLog
index aab3c9b597..74c6a4d94c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Mar 13 09:43:23 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* include/ruby/win32.h (O_SHARE_DELETE): change to fit Fixnum
+	  limit.  [ruby-core:74285] [Bug #12171]
+
 Sun Mar 13 09:15:45 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* numeric.c (rb_fix2str): fix edge case, accidentally generated
diff --git a/include/ruby/win32.h b/include/ruby/win32.h
index c26aa9d4f9..47f68b8cb2 100644
--- a/include/ruby/win32.h
+++ b/include/ruby/win32.h
@@ -127,7 +127,7 @@ typedef unsigned int uintptr_t;
 
 #define WNOHANG -1
 
-#define O_SHARE_DELETE 0x80000000 /* for rb_w32_open(), rb_w32_wopen() */
+#define O_SHARE_DELETE 0x20000000 /* for rb_w32_open(), rb_w32_wopen() */
 
 typedef int clockid_t;
 #define CLOCK_REALTIME  0