diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 62de5f2..3cd1d62 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -718,7 +718,8 @@
 
 #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
+             * (Mbed TLS versions from 1.3 to 2.6.0) */
             mac_key_len = transform->maclen;
 #endif
         }