diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index da21db2..faa9467 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -7092,6 +7092,11 @@
 {
     size_t max_len = MBEDTLS_SSL_OUT_CONTENT_LEN;
 
+#if !defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH) && \
+    !defined(MBEDTLS_SSL_PROTO_DTLS)
+    (void) ssl;
+#endif
+
 #if defined(MBEDTLS_SSL_MAX_FRAGMENT_LENGTH)
     const size_t mfl = mbedtls_ssl_get_max_frag_len( ssl );