diff --git a/ci/python-package.yml b/ci/python-package.yml
index 403cecd..d2278f2 100644
--- a/ci/python-package.yml
+++ b/ci/python-package.yml
@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [3.5, 3.6, 3.7, 3.8]
+        python-version: ['3.5', '3.6', '3.7', '3.8']
 
     steps:
     - uses: actions/checkout@v2