diff --git a/requirements-doc.txt b/requirements-doc.txt
index b7bb6be6..c7db0680 100644
--- a/requirements-doc.txt
+++ b/requirements-doc.txt
@@ -1,4 +1,4 @@
-sphinx
+sphinx==1.5.6
 sphinx_rtd_theme>=0.2.5b1
 sphinx_autobuild
 sphinxcontrib-disqus