diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index d702d3901..42d2388c8 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,8 @@
+2009-03-12  Corinna Vinschen  <corinna@vinschen.de>
+
+	* flock.cc (fhandler_disk_file::lock): Don't test file open mode in
+	case of flock-type locks.  Explain why.
+
 2009-03-12  Brian Ford <Brian.Ford@FlightSafety.com>
 
 	* gethostby_helper: Fix typos in DEBUGGING case.
diff --git a/winsup/cygwin/flock.cc b/winsup/cygwin/flock.cc
index 42941cb78..964156ca0 100644
--- a/winsup/cygwin/flock.cc
+++ b/winsup/cygwin/flock.cc
@@ -652,14 +652,19 @@ fhandler_disk_file::lock (int a_op, struct __flock64 *fl)
 	a_op = F_UNLCK;
 	break;
       case F_RDLCK:
-	if (!(get_access () & GENERIC_READ))
+	/* flock semantics don't specify a requirement that the file has
+	   been opened with a specific open mode, in contrast to POSIX locks
+	   which require that a file is opened for reading to place a read
+	   lock and opened for writing to place a write lock. */
+	if ((a_flags & F_POSIX) && !(get_access () & GENERIC_READ))
 	  {
 	    set_errno (EBADF);
 	    return -1;
 	  }
 	break;
       case F_WRLCK:
-	if (!(get_access () & GENERIC_WRITE))
+	/* See above comment. */
+	if ((a_flags & F_POSIX) && !(get_access () & GENERIC_WRITE))
 	  {
 	    set_errno (EBADF);
 	    return -1;