diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index 91c2058..505f8dd 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -1461,7 +1461,7 @@
      * ...
      */
     MBEDTLS_SSL_CHK_BUF_READ_PTR( p, end, 1 );
-    if( p[0] != 0 )
+    if( p[0] != MBEDTLS_SSL_COMPRESS_NULL )
     {
         MBEDTLS_SSL_DEBUG_MSG( 1, ( "bad legacy compression method" ) );
         fatal_alert = MBEDTLS_SSL_ALERT_MSG_ILLEGAL_PARAMETER;