diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index abafe4d..e25b08d 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1530,6 +1530,8 @@
 #if defined(MBEDTLS_SSL_ENCRYPT_THEN_MAC)
         if( auth_done == 0 )
         {
+            unsigned char mac[MBEDTLS_SSL_MAC_ADD];
+
             /*
              * MAC(MAC_write_key, seq_num +
              *     TLSCipherText.type +
@@ -1552,10 +1554,12 @@
             mbedtls_md_hmac_update( &ssl->transform_out->md_ctx_enc, pseudo_hdr, 13 );
             mbedtls_md_hmac_update( &ssl->transform_out->md_ctx_enc,
                              ssl->out_iv, ssl->out_msglen );
-            mbedtls_md_hmac_finish( &ssl->transform_out->md_ctx_enc,
-                             ssl->out_iv + ssl->out_msglen );
+            mbedtls_md_hmac_finish( &ssl->transform_out->md_ctx_enc, mac );
             mbedtls_md_hmac_reset( &ssl->transform_out->md_ctx_enc );
 
+            memcpy( ssl->out_iv + ssl->out_msglen, mac,
+                    ssl->transform_out->maclen );
+
             ssl->out_msglen += ssl->transform_out->maclen;
             auth_done++;
         }