diff --git a/sys/kern/vfs_mount.c b/sys/kern/vfs_mount.c
--- a/sys/kern/vfs_mount.c
+++ b/sys/kern/vfs_mount.c
@@ -1024,7 +1024,7 @@
 			    fsoptions->uio_iov[2 * errmsg_pos + 1].iov_base,
 			    fsoptions->uio_iov[2 * errmsg_pos + 1].iov_len);
 		} else {
-			copyout(errmsg,
+			(void)copyout(errmsg,
 			    fsoptions->uio_iov[2 * errmsg_pos + 1].iov_base,
 			    fsoptions->uio_iov[2 * errmsg_pos + 1].iov_len);
 		}