diff --git a/lib/ngtcp2_pkt.c b/lib/ngtcp2_pkt.c
index e2d4371e05244fd7a20f87047af6ceacf9fe2c84..905af29a8226020ef5eec1ddb0de5fa48883dcbc 100644
--- a/lib/ngtcp2_pkt.c
+++ b/lib/ngtcp2_pkt.c
@@ -474,6 +474,7 @@ ngtcp2_ssize ngtcp2_pkt_decode_frame(ngtcp2_frame *dest, const uint8_t *payload,
     return ngtcp2_pkt_decode_stop_sending_frame(&dest->stop_sending, payload,
                                                 payloadlen);
   case NGTCP2_FRAME_ACK:
+  case NGTCP2_FRAME_ACK_ECN:
     return ngtcp2_pkt_decode_ack_frame(&dest->ack, payload, payloadlen);
   case NGTCP2_FRAME_PATH_CHALLENGE:
     return ngtcp2_pkt_decode_path_challenge_frame(&dest->path_challenge,