diff --git a/flake.nix b/flake.nix
index 1930e18..6e5cfea 100644
--- a/flake.nix
+++ b/flake.nix
@@ -30,6 +30,7 @@
           ];
           doCheck = true;
           checkPhase = ''
+            export PYTHONPATH="${toString ./src}:$PYTHONPATH"
             python -m pytest tests/ -x --tb=short -q
           '';
           pyproject = true;