diff --git a/src/deepali/core/enum.py b/src/deepali/core/enum.py
index d582517..7c36b93 100644
--- a/src/deepali/core/enum.py
+++ b/src/deepali/core/enum.py
@@ -206,12 +206,12 @@ def is_mixed(key: SpatialDerivativeKey) -> bool:
         return len(set(key)) > 1
 
     @staticmethod
-    def all(ndim: int, order: Union[int, Sequence[int]]) -> List[SpatialDerivativeKey]:
+    def all(spatial_dims: int, order: Union[int, Sequence[int]]) -> List[SpatialDerivativeKey]:
         r"""Unmixed spatial derivatives of specified order."""
         if isinstance(order, int):
             order = [order]
         keys = []
-        dims = [str(SpatialDim(d)) for d in range(ndim)]
+        dims = [str(SpatialDim(d)) for d in range(spatial_dims)]
         for n in order:
             if n > 0:
                 codes = dims
@@ -221,11 +221,11 @@ def all(ndim: int, order: Union[int, Sequence[int]]) -> List[SpatialDerivativeKe
         return keys
 
     @staticmethod
-    def unmixed(ndim: int, order: int) -> List[SpatialDerivativeKey]:
+    def unmixed(spatial_dims: int, order: int) -> List[SpatialDerivativeKey]:
         r"""Unmixed spatial derivatives of specified order."""
         if order <= 0:
             return []
-        return [SpatialDim(d).symbol() * order for d in range(ndim)]
+        return [SpatialDim(d).symbol() * order for d in range(spatial_dims)]
 
     @classmethod
     def unique(cls, keys: Iterable[SpatialDerivativeKey]) -> Set[SpatialDerivativeKey]:
@@ -466,7 +466,7 @@ def all(
         if order == 0:
             return []
         channels = cls._channels(spatial_dims, channel)
-        derivs = SpatialDerivativeKeys.all(spatial_dims, order=order)
+        derivs = SpatialDerivativeKeys.all(spatial_dims=spatial_dims, order=order)
         return [cls.symbol(c, d) for c, d in itertools.product(channels, derivs)]
 
     @classmethod
@@ -482,7 +482,7 @@ def unmixed(
         if order == 0:
             return []
         channels = cls._channels(spatial_dims, channel)
-        derivs = SpatialDerivativeKeys.unmixed(spatial_dims, order=order)
+        derivs = SpatialDerivativeKeys.unmixed(spatial_dims=spatial_dims, order=order)
         return [cls.symbol(c, d) for c, d in itertools.product(channels, derivs)]
 
     @classmethod
@@ -504,7 +504,7 @@ def divergence(cls, spatial_dims: int) -> List[FlowDerivativeKey]:
     @classmethod
     def curvature(cls, spatial_dims: int) -> List[FlowDerivativeKey]:
         channels = range(spatial_dims)
-        derivs = SpatialDerivativeKeys.unmixed(spatial_dims, order=2)
+        derivs = SpatialDerivativeKeys.unmixed(spatial_dims=spatial_dims, order=2)
         return [cls.symbol(c, d) for c, d in itertools.product(channels, derivs)]
 
     @classmethod
diff --git a/src/deepali/core/image.py b/src/deepali/core/image.py
index ecc63f6..9f19786 100644
--- a/src/deepali/core/image.py
+++ b/src/deepali/core/image.py
@@ -1536,7 +1536,7 @@ def spatial_derivatives(
     if which is None:
         if order is None:
             order = 1
-        which = SpatialDerivativeKeys.all(ndim=D, order=order)
+        which = SpatialDerivativeKeys.all(spatial_dims=D, order=order)
     elif order is not None:
         which = [arg for arg in which if len(arg) == order]
 
diff --git a/tests/test_core_enum.py b/tests/test_core_enum.py
index a7a1e19..5a6e065 100644
--- a/tests/test_core_enum.py
+++ b/tests/test_core_enum.py
@@ -74,7 +74,7 @@ def test_flow_derivative_keys_unique() -> None:
 def test_flow_derivative_keys_all() -> None:
     for d, order in itertools.product([2, 3], [0, 1, 2]):
         channel_keys = ["u", "v", "w"][:d]
-        spatial_keys = SpatialDerivativeKeys.all(ndim=d, order=order)
+        spatial_keys = SpatialDerivativeKeys.all(spatial_dims=d, order=order)
         expected = [f"d{a}/d{b}" for a, b in itertools.product(channel_keys, spatial_keys)]
         assert FlowDerivativeKeys.all(spatial_dims=d, order=order) == expected