diff --git a/library/ssl_tls13_generic.c b/library/ssl_tls13_generic.c
index 9c45d2a05..893de4394 100644
--- a/library/ssl_tls13_generic.c
+++ b/library/ssl_tls13_generic.c
@@ -812,7 +812,7 @@ static int ssl_tls13_write_certificate_body( mbedtls_ssl_context *ssl,
         /* Currently, we don't have any certificate extensions defined.
          * Hence, we are sending an empty extension with length zero.
          */
-        MBEDTLS_PUT_UINT24_BE( 0, p, 0 );
+        MBEDTLS_PUT_UINT16_BE( 0, p, 0 );
         p += 2;
     }