diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index c87aee3ce..5dd666ff8 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,8 @@
+2015-02-11  Corinna Vinschen  <corinna@vinschen.de>
+
+	* flock.cc (fhandler_base::lock): Convert accidental system_printf to
+	debug_printf in case of non-matching file modes.  Clear up debug output.
+
 2015-02-11  Corinna Vinschen  <corinna@vinschen.de>
 
 	* dlfcn.cc (check_path_access): Drop FE_NATIVE from find_exec call.
diff --git a/winsup/cygwin/flock.cc b/winsup/cygwin/flock.cc
index 783bf327d..2332f5467 100644
--- a/winsup/cygwin/flock.cc
+++ b/winsup/cygwin/flock.cc
@@ -989,7 +989,7 @@ fhandler_base::lock (int a_op, struct flock *fl)
 	if ((a_flags & F_POSIX)
 	    && ((get_flags () & O_ACCMODE) == O_WRONLY))
 	  {
-	    system_printf ("get_access() == %x", get_access ());
+	    debug_printf ("request F_RDLCK on O_WRONLY file: EBADF");
 	    set_errno (EBADF);
 	    return -1;
 	  }
@@ -999,7 +999,7 @@ fhandler_base::lock (int a_op, struct flock *fl)
 	if ((a_flags & F_POSIX)
 	    && ((get_flags () & O_ACCMODE) == O_RDONLY))
 	  {
-	    system_printf ("get_access() == %x", get_access ());
+	    debug_printf ("request F_WRLCK on O_RDONLY file: EBADF");
 	    set_errno (EBADF);
 	    return -1;
 	  }