diff --git a/sbin/route/route.c b/sbin/route/route.c
--- a/sbin/route/route.c
+++ b/sbin/route/route.c
@@ -1338,6 +1338,20 @@
 			errx(EX_NOHOST, "bad mask length: %s", q + 1);
 
 		inet_makemask((struct sockaddr_in *)&so[RTAX_NETMASK],masklen);
+
+		/*
+		 * Check for bogus destination such as "10/8"; heuristic is
+		 * that there are bits set in the host part, and no dot
+		 * is present.
+		 */
+		if ((ntohl(sin->sin_addr.s_addr) &
+		    ~ntohl(((struct sockaddr_in *)
+		    &so[RTAX_NETMASK])->sin_addr.s_addr)) != 0 &&
+		    strchr(str, '.') == NULL)
+			errx(EX_NOHOST,
+			    "malformed address, bits set after mask;"
+			    " %s means %s",
+			    str, inet_ntoa(sin->sin_addr));
 		return (0);
 	}
 	if (inet_aton(str, &sin->sin_addr) != 0)