diff --git a/taskcluster/config.yml b/taskcluster/config.yml
index fd6eeedaa..60d32c40c 100644
--- a/taskcluster/config.yml
+++ b/taskcluster/config.yml
@@ -8,6 +8,7 @@ treeherder:
         'doc': 'Documentation tasks'
         'unit': 'Unit test tasks'
         'unit-multithread': 'Unit test tasks with multithreading enabled'
+        'unit-serial': 'Unit test tasks with serial enabled'
         'integration': 'Integration test tasks'
 
 index:
diff --git a/taskcluster/kinds/test/linux.yml b/taskcluster/kinds/test/linux.yml
index c0b3b8280..94f73ba58 100644
--- a/taskcluster/kinds/test/linux.yml
+++ b/taskcluster/kinds/test/linux.yml
@@ -70,6 +70,26 @@ unit-multithread:
         command: >-
             uv run coverage run --data-file /builds/worker/artifacts/coverage --context=py{matrix[python]} -m pytest -vv
 
+unit-serial:
+    description: "Run unit tests with py{matrix[python]} on Linux in serial mode"
+    matrix:
+        set-name: "unit-serial-py{matrix[python]}"
+        substitution-fields: [description, run.command, treeherder, worker, attributes]
+        python: ["314"]
+    worker:
+        docker-image: {in-tree: python}
+        env:
+            TASKGRAPH_SERIAL: "1"
+        artifacts:
+            - type: file
+              path: "/builds/worker/artifacts/coverage"
+              name: "public/coverage.py{matrix[python]}"
+    treeherder:
+        symbol: unit-serial(py{matrix[python]})
+    run:
+        command: >-
+            uv run coverage run --data-file /builds/worker/artifacts/coverage --context=py{matrix[python]} -m pytest -vv
+
 integration:
     description: "Run unit tests with py{matrix[python]} on Linux with resolution {matrix[resolution]}"
     attributes:
diff --git a/test/test_generator.py b/test/test_generator.py
index 2024f6178..ed2af30b7 100644
--- a/test/test_generator.py
+++ b/test/test_generator.py
@@ -23,6 +23,9 @@
     not os.environ.get("TASKGRAPH_USE_THREADS"),
     reason="requires multithreading to be enabled",
 )
+asynconly = pytest.mark.skipif(
+    os.environ.get("TASKGRAPH_SERIAL"), reason="requires TASKGRAPH_SERIAL to be 0"
+)
 
 
 class FakePPE(ProcessPoolExecutor):
@@ -42,6 +45,7 @@ def submit(self, kind_load_tasks, *args):
 
 
 @linuxonly
+@asynconly
 def test_kind_ordering_multiprocess(mocker, maketgg):
     "When task kinds depend on each other, they are loaded in postorder"
     mocked_ppe = mocker.patch.object(generator, "ProcessPoolExecutor", new=FakePPE)
@@ -57,6 +61,7 @@ def test_kind_ordering_multiprocess(mocker, maketgg):
 
 
 @threadsonly
+@asynconly
 def test_kind_ordering_multithread(mocker, maketgg):
     "When task kinds depend on each other, they are loaded in postorder"
     mocked_tpe = mocker.patch.object(generator, "ThreadPoolExecutor", new=FakeTPE)