diff --git a/pympipool/flux/executor.py b/pympipool/flux/executor.py
index 95425118..eea42163 100644
--- a/pympipool/flux/executor.py
+++ b/pympipool/flux/executor.py
@@ -27,7 +27,7 @@ class PyFluxExecutor(ExecutorBase):
 
     def __init__(
         self,
-        max_workers,
+        max_workers=1,
         cores_per_worker=1,
         threads_per_core=1,
         gpus_per_worker=0,
diff --git a/pympipool/mpi/executor.py b/pympipool/mpi/executor.py
index 5d137789..8d49b464 100644
--- a/pympipool/mpi/executor.py
+++ b/pympipool/mpi/executor.py
@@ -21,7 +21,7 @@ class PyMPIExecutor(ExecutorBase):
 
     def __init__(
         self,
-        max_workers,
+        max_workers=1,
         cores_per_worker=1,
         oversubscribe=False,
         init_function=None,
diff --git a/pympipool/slurm/executor.py b/pympipool/slurm/executor.py
index 33688506..09316ca6 100644
--- a/pympipool/slurm/executor.py
+++ b/pympipool/slurm/executor.py
@@ -31,7 +31,7 @@ class PySlurmExecutor(ExecutorBase):
 
     def __init__(
         self,
-        max_workers,
+        max_workers=1,
         cores_per_worker=1,
         threads_per_core=1,
         gpus_per_worker=0,