diff --git a/doc/requirements.txt b/doc/requirements.txt
index 085b3a7..b510d7c 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,2 +1,3 @@
-sphinx
+# Pinned due to https://github.com/sphinx-doc/sphinx/issues/5419
+sphinx==1.7.9
 recommonmark