diff --git a/concurrency/README.md b/concurrency/README.md
index 71f0a64..912cc33 100644
--- a/concurrency/README.md
+++ b/concurrency/README.md
@@ -2,7 +2,7 @@
 
 * [Everything You Always Wanted to Know About Synchronization but Were Afraid to Ask](http://sigops.org/sosp/sosp13/papers/p33-david.pdf)
 
-* [Time, Clocks, and the Ordering of Events in a Distributed System](http://lamport.azurewebsites.net/pubs/time-clocks.pdf)
+* [Time, Clocks, and the Ordering of Events in a Distributed System](https://lamport.azurewebsites.net/pubs/time-clocks.pdf)
 
 * [Heap Architectures For Concurrent Languages Using Message Passing](http://www.fantasi.se/publications/ISMM02.pdf)