diff --git a/docs/requirements.txt b/docs/requirements.txt
index 1ba01dcf..5cf3404a 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -1,6 +1,6 @@
 ###### Requirements without Version Specifiers ######
 ipykernel==5.1.0
 nbsphinx==0.4.2
-numpydoc
+numpydoc==0.9.1
 sphinx_bootstrap_theme==0.7.1