diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index 1a739d5f8..364a2ba31 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,8 @@
+2015-01-08  Corinna Vinschen  <corinna@vinschen.de>
+
+	* include/cygwin/socket.h (struct cmsghdr): Redefine cmsg_len as type
+	size_t.  Add comment to explain why.
+
 2015-01-08  Corinna Vinschen  <corinna@vinschen.de>
 
 	* localtime.cc (__cygwin_gettzoffset): New function for access from
diff --git a/winsup/cygwin/include/cygwin/socket.h b/winsup/cygwin/include/cygwin/socket.h
index 8288c8320..b74ada7eb 100644
--- a/winsup/cygwin/include/cygwin/socket.h
+++ b/winsup/cygwin/include/cygwin/socket.h
@@ -1,7 +1,7 @@
 /* cygwin/socket.h
 
    Copyright 1999, 2000, 2001, 2002, 2003, 2005, 2006, 2007, 2009, 2010, 2012,
-   2013, 2014 Red Hat, Inc.
+   2013, 2014, 2015 Red Hat, Inc.
 
 This file is part of Cygwin.
 
@@ -77,7 +77,10 @@ struct msghdr
 
 struct cmsghdr
 {
-  socklen_t		cmsg_len;	/* Length of cmsghdr + data	*/
+  /* Amazing but true: The type of cmsg_len should be socklen_t but, just
+     as on Linux, the definition of the kernel is incompatible with this,
+     so the Windows socket headers define cmsg_len as SIZE_T. */
+  size_t		cmsg_len;	/* Length of cmsghdr + data	*/
   int			cmsg_level;	/* Protocol			*/
   int			cmsg_type;	/* Protocol type		*/
 };