--- a/sys/ddb/db_input.c
+++ b/sys/ddb/db_input.c
@@ -264,7 +264,8 @@
 		*db_le++ = c;
 		return (1);
 	    default:
-		if (db_le == db_lbuf_end) {
+		if (db_le >= db_lbuf_end - 2) {
+		    /* keep room for the trailing '\n' and NUL */
 		    cnputc('\007');
 		}
 		else if (c >= ' ' && c <= '~') {