diff --git a/ip/iptunnel.c b/ip/iptunnel.c
index 40186d3..8479c72 100644
--- a/ip/iptunnel.c
+++ b/ip/iptunnel.c
@@ -240,8 +240,9 @@
 		}
 	}
 
-	if (p->iph.protocol == IPPROTO_IPIP || p->iph.protocol == IPPROTO_IPV6) {
-		if ((p->i_flags & GRE_KEY) || (p->o_flags & GRE_KEY)) {
+	if ((p->i_flags & GRE_KEY) || (p->o_flags & GRE_KEY)) {
+		if (!(p->i_flags & VTI_ISVTI) &&
+		    (p->iph.protocol != IPPROTO_GRE)) {
 			fprintf(stderr, "Keys are not allowed with ipip and sit tunnels\n");
 			return -1;
 		}