diff --git a/ssl/tls13_client.c b/ssl/tls13_client.c
index 87ccdc4..3b85442 100644
--- a/ssl/tls13_client.c
+++ b/ssl/tls13_client.c
@@ -41,6 +41,7 @@
   state_send_client_certificate,
   state_send_client_certificate_verify,
   state_complete_client_certificate_verify,
+  state_send_channel_id,
   state_send_client_finished,
   state_flush,
   state_done,
@@ -519,7 +520,7 @@
 static enum ssl_hs_wait_t do_certificate_callback(SSL *ssl, SSL_HANDSHAKE *hs) {
   /* The peer didn't request a certificate. */
   if (!ssl->s3->hs->cert_request) {
-    hs->state = state_send_client_finished;
+    hs->state = state_send_channel_id;
     return ssl_hs_ok;
   }
 
@@ -566,13 +567,13 @@
                                                             int is_first_run) {
   /* Don't send CertificateVerify if there is no certificate. */
   if (!ssl_has_certificate(ssl)) {
-    hs->state = state_send_client_finished;
+    hs->state = state_send_channel_id;
     return ssl_hs_ok;
   }
 
   switch (tls13_prepare_certificate_verify(ssl, is_first_run)) {
     case ssl_private_key_success:
-      hs->state = state_send_client_finished;
+      hs->state = state_send_channel_id;
       return ssl_hs_write_message;
 
     case ssl_private_key_retry:
@@ -587,6 +588,32 @@
   return ssl_hs_error;
 }
 
+static enum ssl_hs_wait_t do_send_channel_id(SSL *ssl, SSL_HANDSHAKE *hs) {
+  if (!ssl->s3->tlsext_channel_id_valid) {
+    hs->state = state_send_client_finished;
+    return ssl_hs_ok;
+  }
+
+  if (!ssl_do_channel_id_callback(ssl)) {
+    return ssl_hs_error;
+  }
+
+  if (ssl->tlsext_channel_id_private == NULL) {
+    return ssl_hs_channel_id_lookup;
+  }
+
+  CBB cbb, body;
+  if (!ssl->method->init_message(ssl, &cbb, &body, SSL3_MT_CHANNEL_ID) ||
+      !tls1_write_channel_id(ssl, &body) ||
+      !ssl->method->finish_message(ssl, &cbb)) {
+    CBB_cleanup(&cbb);
+    return ssl_hs_error;
+  }
+
+  hs->state = state_send_client_finished;
+  return ssl_hs_write_message;
+}
+
 static enum ssl_hs_wait_t do_send_client_finished(SSL *ssl, SSL_HANDSHAKE *hs) {
   if (!tls13_prepare_finished(ssl)) {
     return ssl_hs_error;
@@ -651,10 +678,13 @@
         break;
       case state_send_client_certificate_verify:
         ret = do_send_client_certificate_verify(ssl, hs, 1 /* first run */);
-      break;
+        break;
       case state_complete_client_certificate_verify:
         ret = do_send_client_certificate_verify(ssl, hs, 0 /* complete */);
-      break;
+        break;
+      case state_send_channel_id:
+        ret = do_send_channel_id(ssl, hs);
+        break;
       case state_send_client_finished:
         ret = do_send_client_finished(ssl, hs);
         break;