diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 73e9c23..498593e 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -36,7 +36,7 @@ jobs:
           auto-update-conda: false
           python-version: ${{ matrix.python-version }}
           channels: conda-forge,nodefaults
-          mamba-version: "*"
+          miniforge-variant: Mambaforge
 
       - name: Install core dependencies.
         shell: bash -l {0}
diff --git a/tests/test_config.py b/tests/test_config.py
index 817713f..9f37753 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -35,16 +35,17 @@ def test_interplay_between_debugging_and_parallel(tmp_path, pdb, n_workers, expe
         ("parallel_backend", "unknown_backend", ExitCode.CONFIGURATION_FAILED),
     ]
     + [
-        ("parallel_backend", parallel_backend.value, ExitCode.OK)
+        ("parallel_backend", parallel_backend, ExitCode.OK)
         for parallel_backend in ParallelBackendChoices
     ],
 )
 def test_reading_values_from_config_file(
     tmp_path, configuration_option, value, exit_code
 ):
+    config_value = value.value if isinstance(value, ParallelBackendChoices) else value
     config = f"""
     [tool.pytask.ini_options]
-    {configuration_option} = {value!r}
+    {configuration_option} = {config_value!r}
     """
     tmp_path.joinpath("pyproject.toml").write_text(textwrap.dedent(config))
 
diff --git a/tests/test_execute.py b/tests/test_execute.py
index 959838c..fbad52a 100644
--- a/tests/test_execute.py
+++ b/tests/test_execute.py
@@ -11,6 +11,7 @@
 from pytask import main
 from pytask import Task
 from pytask_parallel.backends import PARALLEL_BACKENDS
+from pytask_parallel.backends import ParallelBackendChoices
 from pytask_parallel.execute import _Sleeper
 from pytask_parallel.execute import DefaultBackendNameSpace
 from pytask_parallel.execute import ProcessesNameSpace
@@ -129,9 +130,9 @@ def myfunc():
         session.config["_parallel_executor"] = executor
 
         backend_name_space = {
-            "processes": ProcessesNameSpace,
-            "threads": DefaultBackendNameSpace,
-            "loky": DefaultBackendNameSpace,
+            ParallelBackendChoices.PROCESSES: ProcessesNameSpace,
+            ParallelBackendChoices.THREADS: DefaultBackendNameSpace,
+            ParallelBackendChoices.LOKY: DefaultBackendNameSpace,
         }[parallel_backend]
 
         future = backend_name_space.pytask_execute_task(session, task)
@@ -269,7 +270,11 @@ def task_example(produces):
 @pytest.mark.parametrize(
     "parallel_backend",
     # Capturing warnings is not thread-safe.
-    [backend for backend in PARALLEL_BACKENDS if backend != "threads"],
+    [
+        backend
+        for backend in PARALLEL_BACKENDS
+        if backend != ParallelBackendChoices.THREADS
+    ],
 )
 def test_collect_warnings_from_parallelized_tasks(runner, tmp_path, parallel_backend):
     source = """