diff --git a/docs/requirements.txt b/docs/requirements.txt
index a3b2106..874e6a8 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -5,6 +5,7 @@ readthedocs-sphinx-search
 sphinx_autodoc_typehints==1.12.0
 numpy
 typing_extensions
+vtkmodules
 --pre cadquery-ocp
 -e git+https://github.com/gumyr/build123d.git#egg=build123d
 sphinx_design