diff --git a/conf.c b/conf.c
index 14356b7..cddc769 100644
--- a/conf.c
+++ b/conf.c
@@ -257,6 +257,7 @@ static int conf_ports(struct ctx *c, char optname, const char *optarg,
 
 				bitmap_set(exclude, i);
 			}
+			start_src = end_src = -1;
 			break;
 		default:
 			goto bad;