diff --git a/.github/workflows/check.yml b/.github/workflows/check.yml
index 881fa20..b4cdffb 100644
--- a/.github/workflows/check.yml
+++ b/.github/workflows/check.yml
@@ -14,7 +14,7 @@ concurrency:
 
 jobs:
   test:
-    name: test ${{ matrix.py }}
+    name: test ${{ matrix.py }} on ${{ matrix.os }}
     runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
diff --git a/src/tox_uv/_venv.py b/src/tox_uv/_venv.py
index c5ee31c..c65f5a5 100644
--- a/src/tox_uv/_venv.py
+++ b/src/tox_uv/_venv.py
@@ -63,7 +63,7 @@ def _get_python(self, base_python: list[str]) -> PythonInfo | None:  # noqa: PLR
                 )
             spec = PythonSpec.from_string_spec(base)
             return PythonInfo(
-                implementation=spec.implementation,
+                implementation=spec.implementation or "CPython",
                 version_info=VersionInfo(
                     major=spec.major,
                     minor=spec.minor,