diff --git a/ChangeLog b/ChangeLog
index 0cd5fe5c0e..2fa95e8d56 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Mon Apr  5 13:20:45 2010  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* include/ruby/win32.h, win32/win32.c (EWOULDBLOCK): VC10 already
+	  defined EWOULDBLOCK.  based on a patch from Charlie Savage,
+	  see [ruby-core:29255]
+
 Mon Apr  5 13:10:35 2010  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* ext/psych/lib/psych/core_ext.rb: remove before alias.
diff --git a/include/ruby/win32.h b/include/ruby/win32.h
index aa8b2c26ce..ec3385a33f 100644
--- a/include/ruby/win32.h
+++ b/include/ruby/win32.h
@@ -401,7 +401,9 @@ extern char *rb_w32_strerror(int);
 /* #undef va_end */
 
 /* winsock error map */
+#ifndef EWOULDBLOCK	/* VC10 has this */
 #define EWOULDBLOCK	WSAEWOULDBLOCK
+#endif
 #define EINPROGRESS	WSAEINPROGRESS
 #define EALREADY	WSAEALREADY
 #define ENOTSOCK	WSAENOTSOCK
diff --git a/win32/win32.c b/win32/win32.c
index 42fbdb591b..020eb6bab8 100644
--- a/win32/win32.c
+++ b/win32/win32.c
@@ -161,7 +161,7 @@ static struct {
     {	ERROR_PIPE_NOT_CONNECTED,	EPIPE		},
     {	ERROR_OPERATION_ABORTED,	EINTR		},
     {	ERROR_NOT_ENOUGH_QUOTA,		ENOMEM		},
-    {	ERROR_MOD_NOT_FOUND,		ENOENT          },
+    {	ERROR_MOD_NOT_FOUND,		ENOENT		},
     {	WSAENAMETOOLONG,		ENAMETOOLONG	},
     {	WSAENOTEMPTY,			ENOTEMPTY	},
     {	WSAEINTR,			EINTR		},
@@ -170,6 +170,7 @@ static struct {
     {	WSAEFAULT,			EFAULT		},
     {	WSAEINVAL,			EINVAL		},
     {	WSAEMFILE,			EMFILE		},
+    {	WSAEWOULDBLOCK,			EWOULDBLOCK	},
 };
 
 int