diff --git a/atomistics/workflows/evcurve/workflow.py b/atomistics/workflows/evcurve/workflow.py
index 22cc4843..ed006d94 100644
--- a/atomistics/workflows/evcurve/workflow.py
+++ b/atomistics/workflows/evcurve/workflow.py
@@ -1,6 +1,5 @@
 import numpy as np
 from ase.atoms import Atoms
-from typing import Literal
 from collections import OrderedDict
 
 from atomistics.workflows.evcurve.fit import EnergyVolumeFit
@@ -8,7 +7,7 @@
 
 
 def _strain_axes(
-    structure: Atoms, axes: Literal["x", "y", "z"], volume_strain: float
+    structure: Atoms, volume_strain: float, axes: tuple[str, str, str] = ("x", "y", "z")
 ) -> Atoms:
     """
     Strain box along given axes to achieve given *volumetric* strain.
@@ -75,7 +74,7 @@ def __init__(
         fit_type="polynomial",
         fit_order=3,
         vol_range=0.05,
-        axes=["x", "y", "z"],
+        axes=("x", "y", "z"),
         strains=None,
     ):
         self.structure = structure
@@ -106,7 +105,9 @@ def generate_structures(self):
                 int(self.num_points),
             )
         for strain in strains:
-            basis = _strain_axes(self.structure, self.axes, strain)
+            basis = _strain_axes(
+                structure=self.structure, axes=self.axes, volume_strain=strain
+            )
             self._structure_dict[1 + np.round(strain, 7)] = basis
         return {"calc_energy": self._structure_dict}
 
diff --git a/tests/test_evcurve_abinit.py b/tests/test_evcurve_abinit.py
index c5c91739..28a9dacb 100644
--- a/tests/test_evcurve_abinit.py
+++ b/tests/test_evcurve_abinit.py
@@ -40,7 +40,7 @@ def test_calc_evcurve(self):
             fit_type='polynomial',
             fit_order=3,
             vol_range=0.05,
-            axes=['x', 'y', 'z'],
+            axes=('x', 'y', 'z'),
             strains=None,
         )
         task_dict = workflow.generate_structures()
diff --git a/tests/test_evcurve_emt.py b/tests/test_evcurve_emt.py
index 4c45b0eb..405fc8f8 100644
--- a/tests/test_evcurve_emt.py
+++ b/tests/test_evcurve_emt.py
@@ -15,7 +15,7 @@ def test_calc_evcurve(self):
             fit_type='polynomial',
             fit_order=3,
             vol_range=0.05,
-            axes=['x', 'y', 'z'],
+            axes=('x', 'y', 'z'),
             strains=None,
         )
         task_dict = workflow.generate_structures()
diff --git a/tests/test_evcurve_gpaw.py b/tests/test_evcurve_gpaw.py
index 7c463e6b..e19b60b1 100644
--- a/tests/test_evcurve_gpaw.py
+++ b/tests/test_evcurve_gpaw.py
@@ -25,7 +25,7 @@ def test_calc_evcurve(self):
             fit_type='polynomial',
             fit_order=3,
             vol_range=0.05,
-            axes=['x', 'y', 'z'],
+            axes=('x', 'y', 'z'),
             strains=None,
         )
         task_dict = workflow.generate_structures()
diff --git a/tests/test_evcurve_lammps.py b/tests/test_evcurve_lammps.py
index 4a1bf797..1d5259e2 100644
--- a/tests/test_evcurve_lammps.py
+++ b/tests/test_evcurve_lammps.py
@@ -41,7 +41,7 @@ def test_calc_evcurve(self):
             fit_type='polynomial',
             fit_order=3,
             vol_range=0.05,
-            axes=['x', 'y', 'z'],
+            axes=('x', 'y', 'z'),
             strains=None,
         )
         task_dict = workflow.generate_structures()
diff --git a/tests/test_evcurve_qe.py b/tests/test_evcurve_qe.py
index dde12eb3..efeeb319 100644
--- a/tests/test_evcurve_qe.py
+++ b/tests/test_evcurve_qe.py
@@ -43,7 +43,7 @@ def test_calc_evcurve(self):
             fit_type='polynomial',
             fit_order=3,
             vol_range=0.05,
-            axes=['x', 'y', 'z'],
+            axes=('x', 'y', 'z'),
             strains=None,
         )
         task_dict = workflow.generate_structures()
diff --git a/tests/test_evcurve_siesta.py b/tests/test_evcurve_siesta.py
index 527af14e..95d5f5ad 100644
--- a/tests/test_evcurve_siesta.py
+++ b/tests/test_evcurve_siesta.py
@@ -44,7 +44,7 @@ def test_calc_evcurve(self):
             fit_type='polynomial',
             fit_order=3,
             vol_range=0.05,
-            axes=['x', 'y', 'z'],
+            axes=('x', 'y', 'z'),
             strains=None,
         )
         task_dict = workflow.generate_structures()