diff --git a/tests/test_integration_pyiron_workflow.py b/tests/test_integration_pyiron_workflow.py
index 37272703..64f0eed6 100644
--- a/tests/test_integration_pyiron_workflow.py
+++ b/tests/test_integration_pyiron_workflow.py
@@ -74,7 +74,7 @@ def slowly_returns_dynamic(dynamic_arg):
             return dynamic_arg
 
         dynamic_dynamic = slowly_returns_dynamic()
-        executor = Executor(block_allocation=True)
+        executor = Executor(block_allocation=True, max_workers=1)
         cloudpickle_register(ind=1)
         dynamic_object = does_nothing()
         fs = executor.submit(dynamic_dynamic.run, dynamic_object)
@@ -104,7 +104,7 @@ def slowly_returns_42():
         self.assertIsNone(
             dynamic_42.result, msg="Just a sanity check that the test is set up right"
         )
-        executor = Executor(block_allocation=True)
+        executor = Executor(block_allocation=True, max_workers=1)
         cloudpickle_register(ind=1)
         fs = executor.submit(dynamic_42.run)
         fs.add_done_callback(dynamic_42.process_result)
@@ -135,7 +135,7 @@ def returns_42():
             dynamic_42.running,
             msg="Sanity check that the test starts in the expected condition",
         )
-        executor = Executor(block_allocation=True)
+        executor = Executor(block_allocation=True, max_workers=1)
         cloudpickle_register(ind=1)
         fs = executor.submit(dynamic_42.run)
         fs.add_done_callback(dynamic_42.process_result)
@@ -159,7 +159,7 @@ def raise_error():
             raise RuntimeError
 
         re = raise_error()
-        executor = Executor(block_allocation=True)
+        executor = Executor(block_allocation=True, max_workers=1)
         cloudpickle_register(ind=1)
         fs = executor.submit(re.run)
         with self.assertRaises(
@@ -189,7 +189,7 @@ def slowly_returns_dynamic():
             return inside_variable
 
         dynamic_dynamic = slowly_returns_dynamic()
-        executor = Executor(block_allocation=True)
+        executor = Executor(block_allocation=True, max_workers=1)
         cloudpickle_register(ind=1)
         fs = executor.submit(dynamic_dynamic.run)
         self.assertIsInstance(
@@ -218,7 +218,7 @@ def slow():
             return fortytwo
 
         f = slow()
-        executor = Executor(block_allocation=True)
+        executor = Executor(block_allocation=True, max_workers=1)
         cloudpickle_register(ind=1)
         fs = executor.submit(f.run)
         self.assertEqual(
diff --git a/tests/test_local_executor_future.py b/tests/test_local_executor_future.py
index 13691579..7ab3f1cd 100644
--- a/tests/test_local_executor_future.py
+++ b/tests/test_local_executor_future.py
@@ -68,6 +68,7 @@ def submit():
                 # Executor only exists in this scope and can get garbage collected after
                 # this function is exits
                 future = InteractiveExecutor(
+                    max_workers=1,
                     executor_kwargs={},
                     spawner=MpiExecSpawner,
                 ).submit(slow_callable)
@@ -108,6 +109,7 @@ def run(self):
                     self.running = True
 
                     future = InteractiveExecutor(
+                        max_workers=1,
                         executor_kwargs={},
                         spawner=MpiExecSpawner,
                     ).submit(self.return_42)
diff --git a/tests/test_shell_interactive.py b/tests/test_shell_interactive.py
index c304e65c..e211b559 100644
--- a/tests/test_shell_interactive.py
+++ b/tests/test_shell_interactive.py
@@ -105,6 +105,7 @@ def test_execute_single_task(self):
     def test_shell_interactive_executor(self):
         cloudpickle_register(ind=1)
         with Executor(
+            max_workers=1,
             init_function=init_process,
             block_allocation=True,
         ) as exe: