diff --git a/docs/requirements-doc.txt b/docs/requirements-doc.txt
index bbccc8b..9157dc6 100644
--- a/docs/requirements-doc.txt
+++ b/docs/requirements-doc.txt
@@ -12,3 +12,4 @@ psutil>=5.9.0
 readme2tex>=0.0.1b2
 dill>=0.3.4
 mistune==0.8.4
+numpydoc>=1.1.0