diff --git a/tests/framework/session/test_session_extension_hooks.py b/tests/framework/session/test_session_extension_hooks.py
index 64d2e4509f..d500e0a5a4 100644
--- a/tests/framework/session/test_session_extension_hooks.py
+++ b/tests/framework/session/test_session_extension_hooks.py
@@ -241,7 +241,7 @@ def test_before_and_after_node_run_hooks_sequential_runner(
     def test_on_node_error_hook_parallel_runner(self, mock_session, logs_listener):
         with pytest.raises(ValueError, match="broken"):
             mock_session.run(
-                runner=ParallelRunner(max_workers=2), node_names=["node1", "node2"]
+                runner=ParallelRunner(max_workers=1), node_names=["node1", "node2"]
             )
 
         on_node_error_records = [
diff --git a/tests/runner/test_thread_runner.py b/tests/runner/test_thread_runner.py
index 8da85624e0..aea7b15b1e 100644
--- a/tests/runner/test_thread_runner.py
+++ b/tests/runner/test_thread_runner.py
@@ -317,7 +317,7 @@ def test_stricter_suggest_resume_scenario(
             test_pipeline += modular_pipeline([nodes[name]._copy(func=exception_fn)])
 
         with pytest.raises(Exception, match="test exception"):
-            ThreadRunner().run(
+            ThreadRunner(max_workers=1).run(
                 test_pipeline,
                 persistent_dataset_catalog,
                 hook_manager=_create_hook_manager(),