diff --git a/usr.bin/config/sem.c b/usr.bin/config/sem.c
index 445c69ed92d8..fc513874efac 100644
--- a/usr.bin/config/sem.c
+++ b/usr.bin/config/sem.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: sem.c,v 1.22 2006/03/29 09:16:36 cube Exp $	*/
+/*	$NetBSD: sem.c,v 1.23 2006/08/07 12:03:32 cube Exp $	*/
 
 /*
  * Copyright (c) 1992, 1993
@@ -1369,6 +1369,12 @@ deldev(const char *name)
 			error("unknown device %s", name);
 			return;
 		}
+		if (d->d_ispseudo) {
+			error("%s is a pseudo-device; "
+			    "use \"no pseudo-device %s\" instead", name,
+			    name);
+			return;
+		}
 
 		for (firsti = d->d_ihead; firsti != NULL;
 		    firsti = firsti->i_bsame)