diff --git a/docs/x509.rst b/docs/x509.rst
index d99fae6..da6bd85 100644
--- a/docs/x509.rst
+++ b/docs/x509.rst
@@ -967,4 +967,4 @@
 
 .. _`public key infrastructure`: https://en.wikipedia.org/wiki/Public_key_infrastructure
 .. _`TLS`: https://en.wikipedia.org/wiki/Transport_Layer_Security
-.. _`RFC 5280 section 4.2.1.1`: http://tools.ietf.org/html/rfc5280#section-4.2.1.1
+.. _`RFC 5280 section 4.2.1.1`: https://tools.ietf.org/html/rfc5280#section-4.2.1.1