diff --git a/usr.sbin/rtadvd/advcap.c b/usr.sbin/rtadvd/advcap.c
index 7280f4097d66..542e06649f92 100644
--- a/usr.sbin/rtadvd/advcap.c
+++ b/usr.sbin/rtadvd/advcap.c
@@ -149,9 +149,9 @@ getent(char *bp, char *name, const char *cfile)
 				}
 				break;
 			}
-			if (cp >= bp + BUFSIZ) {
+			if (cp >= bp + BUFSIZ - 1) {
 				write(STDERR_FILENO, "Remcap entry too long\n",
-				      23);
+				    22);
 				break;
 			} else
 				*cp++ = c;