Index: sys/kern/vfs_vnops.c
===================================================================
RCS file: /cvsroot/src/sys/kern/vfs_vnops.c,v
retrieving revision 1.217
diff -u -p -r1.217 vfs_vnops.c
--- sys/kern/vfs_vnops.c	30 Jun 2021 11:20:32 -0000	1.217
+++ sys/kern/vfs_vnops.c	30 Jun 2021 17:40:27 -0000
@@ -332,9 +332,13 @@ out:
 	case EDUPFD:
 	case EMOVEFD:
 		/* if the caller isn't prepared to handle fds, fail for them */
-		KASSERTMSG(ret_domove && ret_fd,
-		    "caller did not supply ret_domove and ret_fd for %d",
-		    error);
+		if (ret_fd == NULL) {
+			KASSERT(ret_domove == NULL);
+			error = EOPNOTSUPP;
+			break;
+		}
+		KASSERT(ret_domove != NULL);
+		error = 0;
 		*ret_vp = NULL;
 		*ret_domove = error == EMOVEFD;
 		*ret_fd = l->l_dupfd;