===================================================================
RCS file: /cvsrepo/anoncvs/cvs/src/usr.bin/mandoc/roff.c,v
retrieving revision 1.253
retrieving revision 1.254
diff -u -r1.253 -r1.254
--- src/usr.bin/mandoc/roff.c	2022/04/13 13:11:33	1.253
+++ src/usr.bin/mandoc/roff.c	2022/04/24 13:34:53	1.254
@@ -1,4 +1,4 @@
-/* $OpenBSD: roff.c,v 1.253 2022/04/13 13:11:33 schwarze Exp $ */
+/* $OpenBSD: roff.c,v 1.254 2022/04/24 13:34:53 schwarze Exp $ */
 /*
  * Copyright (c) 2010-2015, 2017-2022 Ingo Schwarze <schwarze@openbsd.org>
  * Copyright (c) 2008-2012, 2014 Kristaps Dzonsons <kristaps@bsd.lv>
@@ -3868,8 +3868,9 @@
 roff_shift(ROFF_ARGS)
 {
 	struct mctx	*ctx;
-	int		 levels, i;
+	int		 argpos, levels, i;
 
+	argpos = pos;
 	levels = 1;
 	if (buf->buf[pos] != '\0' &&
 	    roff_evalnum(r, ln, buf->buf, &pos, &levels, 0) == 0) {
@@ -3884,8 +3885,12 @@
 	ctx = r->mstack + r->mstackpos;
 	if (levels > ctx->argc) {
 		mandoc_msg(MANDOCERR_SHIFT,
-		    ln, pos, "%d, but max is %d", levels, ctx->argc);
+		    ln, argpos, "%d, but max is %d", levels, ctx->argc);
 		levels = ctx->argc;
+	}
+	if (levels < 0) {
+		mandoc_msg(MANDOCERR_ARG_NEG, ln, argpos, "shift %d", levels);
+		levels = 0;
 	}
 	if (levels == 0)
 		return ROFF_IGN;