diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 8343f03..a1a6eea 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -69,7 +69,7 @@ jobs:
 
       - name: Install
         run: |
-          poetry run pip install maturin  # pendulum
+          poetry run pip install maturin cython  # pendulum
           poetry install
 
       - name: Style