diff --git a/sys/netinet6/icmp6.c b/sys/netinet6/icmp6.c
--- a/sys/netinet6/icmp6.c
+++ b/sys/netinet6/icmp6.c
@@ -2605,6 +2605,7 @@
 				/* pad if easy enough, truncate if not */
 				if (8 - extra <= M_TRAILINGSPACE(m0)) {
 					/* pad */
+					bzero(m0->m_data + m0->m_len, 8 - extra);
 					m0->m_len += (8 - extra);
 					m0->m_pkthdr.len += (8 - extra);
 				} else {