--- tcpdump-4.9.2/print-hncp.c.old	2017-09-03 23:17:14.000000000 +0000
+++ tcpdump-4.9.2/print-hncp.c	2018-12-07 19:31:24.360000000 +0000
@@ -228,6 +228,7 @@
 	snprintf(buf, sizeof(buf), "%s/%d", ipaddr_string(ndo, &addr), plen);
         plenbytes += 1 + IPV4_MAPPED_HEADING_LEN;
     } else {
+        buf[0] = '\0';
         plenbytes = decode_prefix6(ndo, prefix, max_length, buf, sizeof(buf));
     }