diff --git a/lib/vquic/ngtcp2.c b/lib/vquic/ngtcp2.c
index 764f95778..0788404c0 100644
--- a/lib/vquic/ngtcp2.c
+++ b/lib/vquic/ngtcp2.c
@@ -1601,9 +1601,11 @@ static CURLcode ng_flush_egress(struct connectdata *conn, int sockfd,
   case AF_INET:
     pktlen = NGTCP2_MAX_PKTLEN_IPV4;
     break;
+#ifdef ENABLE_IPV6
   case AF_INET6:
     pktlen = NGTCP2_MAX_PKTLEN_IPV6;
     break;
+#endif
   default:
     assert(0);
   }