diff --git a/.circleci/config.yml b/.circleci/config.yml
index c296f03..b8e78c5 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -30,7 +30,7 @@ jobs:
       - run:
           name: Compile Cython files
           command: |
-            cythonize -i werpy/metrics.pyx
+            cythonize -X language_level=3 -i werpy/metrics.pyx
       - run:  
           name: Run unit tests
           command: python -m unittest discover tests