diff --git a/ci/environment-docs.yml b/ci/environment-docs.yml
index fe39b58c..d06b2376 100644
--- a/ci/environment-docs.yml
+++ b/ci/environment-docs.yml
@@ -32,3 +32,4 @@ dependencies:
   - sphinx
   - numpydoc
   - sphinx-rtd-theme
+  - ujson