diff --git a/library/ecdh.c b/library/ecdh.c
index b529af59c9..58ef881f04 100644
--- a/library/ecdh.c
+++ b/library/ecdh.c
@@ -20,7 +20,7 @@
 /*
  * References:
  *
- * SEC1 http://www.secg.org/index.php?action=secg,docs_secg
+ * SEC1 https://www.secg.org/sec1-v2.pdf
  * RFC 4492
  */