diff --git a/library/hmac_drbg.c b/library/hmac_drbg.c
index dfb3ca3..0f89ede 100644
--- a/library/hmac_drbg.c
+++ b/library/hmac_drbg.c
@@ -3,7 +3,7 @@
  *
  *  Copyright (C) 2014, ARM Limited, All Rights Reserved
  *
- *  This file is part of mbed TLS (http://www.polarssl.org)
+ *  This file is part of mbed TLS (https://www.polarssl.org)
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by