diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2e3aaf0..0423c2e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -36,7 +36,7 @@ jobs:
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names
-        flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics --exclude=Pyxis/doc/example/*
+        flake8 . --count --select=E9,F63,F7,F82,F821 --show-source --statistics --exclude=Pyxis/doc/example/*
         # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide
         flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics --exclude=Pyxis/doc/example/*
     - name: Test with pytest