diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 8bd23ab6..02f85369 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -33,7 +33,7 @@ Or to use a hermetic Docker container:
 ```
 
 This process builds RST documentation directly from the proto files, merges it with the static RST
-files, and then runs [Sphinx](http://www.sphinx-doc.org/en/stable/rest.html) over the entire tree to
+files, and then runs [Sphinx](https://www.sphinx-doc.org/en/stable/rest.html) over the entire tree to
 produce the final documentation. The generated RST files are not committed as they are regenerated
 every time the documentation is built.