diff --git a/afids_utils/tests/test_transforms.py b/afids_utils/tests/test_transforms.py
index c45d0e76..11e107f4 100644
--- a/afids_utils/tests/test_transforms.py
+++ b/afids_utils/tests/test_transforms.py
@@ -1,16 +1,17 @@
 from __future__ import annotations
 
 import numpy as np
+import pytest
 from hypothesis import HealthCheck, given, settings
 from numpy.typing import NDArray
 
 from afids_utils.afids import AfidPosition, AfidVoxel
 from afids_utils.tests.strategies import (
     affine_xfms,
-    world_coords,
     voxel_coords,
+    world_coords,
 )
-from afids_utils.transforms import world_to_voxel, voxel_to_world
+from afids_utils.transforms import voxel_to_world, world_to_voxel
 
 
 class TestAfidWorld2Voxel:
@@ -30,6 +31,17 @@ def test_world_to_voxel_xfm(
         assert isinstance(voxel_coord.j, np.int64)
         assert isinstance(voxel_coord.k, np.int64)
 
+    @given(voxel_coord=voxel_coords(), nii_affine=affine_xfms())
+    @settings(
+        deadline=400,
+        suppress_health_check=[HealthCheck.function_scoped_fixture],
+    )
+    def test_invalid_world_type(
+        self, voxel_coord: AfidVoxel, nii_affine: NDArray[np.float_]
+    ):
+        with pytest.raises(TypeError, match="Not an AfidPosition.*"):
+            world_to_voxel(voxel_coord, nii_affine)
+
 
 class TestAfidVoxel2World:
     @given(voxel_coord=voxel_coords(), nii_affine=affine_xfms())
@@ -47,3 +59,14 @@ def test_voxel_to_world_xfm(
         assert isinstance(world_coord.x, np.float64)
         assert isinstance(world_coord.y, np.float64)
         assert isinstance(world_coord.z, np.float64)
+
+    @given(world_coord=world_coords(), nii_affine=affine_xfms())
+    @settings(
+        deadline=400,
+        suppress_health_check=[HealthCheck.function_scoped_fixture],
+    )
+    def test_invalid_voxel_type(
+        self, world_coord: AfidPosition, nii_affine: NDArray[np.float_]
+    ):
+        with pytest.raises(TypeError, match="Not an AfidVoxel.*"):
+            voxel_to_world(world_coord, nii_affine)
diff --git a/afids_utils/transforms.py b/afids_utils/transforms.py
index e0994b80..e3d7b575 100644
--- a/afids_utils/transforms.py
+++ b/afids_utils/transforms.py
@@ -29,6 +29,8 @@ def world_to_voxel(
     AfidVoxel
         Object containing transformed integer voxel coordinates (i, j, k)
     """
+    if not isinstance(afid_world, AfidPosition):
+        raise TypeError("Not an AfidPosition object")
 
     # Put into numpy array for easier computation
     world_pos = np.asarray([afid_world.x, afid_world.y, afid_world.z])
@@ -69,6 +71,8 @@ def voxel_to_world(
         Object containing approximate floating-point spatial coordinates
         (x, y, z)
     """
+    if not isinstance(afid_voxel, AfidVoxel):
+        raise TypeError("Not an AfidVoxel object")
 
     # Put into numpy array for easier computation
     voxel_pos = np.asarray([afid_voxel.i, afid_voxel.j, afid_voxel.k])