diff --git a/library/ssl_tls13_server.c b/library/ssl_tls13_server.c
index 4dcd609..0159b02 100644
--- a/library/ssl_tls13_server.c
+++ b/library/ssl_tls13_server.c
@@ -1883,7 +1883,7 @@
     psa_hash_alg = mbedtls_psa_translate_md( ciphersuite_info->mac );
     hash_length = PSA_HASH_LENGTH( psa_hash_alg );
     if( hash_length == -1 ||
-        hash_length > (int)sizeof( session->resumption_key ) )
+        (size_t)hash_length > sizeof( session->resumption_key ) )
     {
         return( MBEDTLS_ERR_SSL_INTERNAL_ERROR );
     }