diff --git a/docs/installation.rst b/docs/installation.rst
index 9793ac2..5d629e9 100644
--- a/docs/installation.rst
+++ b/docs/installation.rst
@@ -255,3 +255,4 @@
 .. _`bug in conda`: https://github.com/conda/conda-recipes/issues/110
 .. _`Greg Wilson's blog post`: http://software-carpentry.org/blog/2014/04/mr-biczo-was-right.html
 .. _virtualenv: https://virtualenv.pypa.io/en/latest/
+.. _openssl.org: https://openssl.org/source/