diff --git a/docs/requirements.txt b/docs/requirements.txt
index 1632a96..ff714be 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,4 +1,4 @@
-sphinx
-sphinxcontrib-napoleon
-sphinx-py3doc-enhanced-theme
+sphinx==1.5.3
+sphinxcontrib-napoleon==0.6.1
+sphinx-py3doc-enhanced-theme==2.4.0
 -e .