diff --git a/contrib/libpcap/bpf/net/bpf_filter.c b/contrib/libpcap/bpf/net/bpf_filter.c
index db12bb2bad9e..f172384fa8c8 100644
--- a/contrib/libpcap/bpf/net/bpf_filter.c
+++ b/contrib/libpcap/bpf/net/bpf_filter.c
@@ -405,7 +405,18 @@ bpf_filter(pc, p, wirelen, buflen)
 			continue;
 
 		case BPF_JMP|BPF_JA:
+#if defined(KERNEL) || defined(_KERNEL)
+			/*
+			 * No backward jumps allowed.
+			 */
 			pc += pc->k;
+#else
+			/*
+			 * XXX - we currently implement "ip6 protochain"
+			 * with backward jumps, so sign-extend pc->k.
+			 */
+			pc += (bpf_int32)pc->k;
+#endif
 			continue;
 
 		case BPF_JMP|BPF_JGT|BPF_K: