diff --git a/library/ssl_tls12_client.c b/library/ssl_tls12_client.c
index dd55456..0444f27 100644
--- a/library/ssl_tls12_client.c
+++ b/library/ssl_tls12_client.c
@@ -1137,7 +1137,12 @@
 {
     const unsigned char *p = ssl->in_msg + mbedtls_ssl_hs_hdr_len( ssl );
     uint16_t dtls_legacy_version;
-    unsigned char cookie_len;
+
+#if !defined(MBEDTLS_SSL_PROTO_TLS1_3)
+    uint8_t cookie_len;
+#else
+    uint16_t cookie_len;
+#endif
 
     MBEDTLS_SSL_DEBUG_MSG( 2, ( "=> parse hello verify request" ) );