diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index f0cc95f..c72ee1d 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -719,7 +719,7 @@
 
 #if defined(MBEDTLS_SSL_TRUNCATED_HMAC_COMPAT)
             /* Fall back to old, non-compliant version of the truncated
-             * HMAC implementation which also truncates the key. */
+             * HMAC implementation which also truncates the key (pre 2.1.10) */
             mac_key_len = transform->maclen;
 #endif
         }