Index: head/sys/netinet6/nd6.c
===================================================================
--- head/sys/netinet6/nd6.c
+++ head/sys/netinet6/nd6.c
@@ -821,9 +821,27 @@
 				clear_llinfo_pqueue(ln);
 			}
 			nd6_free(&ln, 0);
-			if (m != NULL)
-				icmp6_error2(m, ICMP6_DST_UNREACH,
-				    ICMP6_DST_UNREACH_ADDR, 0, ifp);
+			if (m != NULL) {
+				struct mbuf *n = m;
+
+				/*
+				 * if there are any ummapped mbufs, we
+				 * must free them, rather than using
+				 * them for an ICMP, as they cannot be
+				 * checksummed.
+				 */
+				while ((n = n->m_next) != NULL) {
+					if (n->m_flags & M_EXTPG)
+						break;
+				}
+				if (n != NULL) {
+					m_freem(m);
+					m = NULL;
+				} else {
+					icmp6_error2(m, ICMP6_DST_UNREACH,
+					    ICMP6_DST_UNREACH_ADDR, 0, ifp);
+				}
+			}
 		}
 		break;
 	case ND6_LLINFO_REACHABLE: