diff --git a/.circleci/config.yml b/.circleci/config.yml
index 08b2fdaad..c4d647cc1 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -32,6 +32,7 @@ jobs:
           command: |
             python3 -m venv venv
             . venv/bin/activate
+            pip install cython
             echo "tox" >> requirements.txt
             pip install -r requirements.txt
             pip install -r requirements-test.txt