diff --git a/meanas/fdmath/functional.py b/meanas/fdmath/functional.py
index 0e90f2b..1b5811d 100644
--- a/meanas/fdmath/functional.py
+++ b/meanas/fdmath/functional.py
@@ -8,7 +8,7 @@ from collections.abc import Sequence, Callable
 
 import numpy
 from numpy.typing import NDArray
-from numpy import floating
+from numpy import floating, complexfloating
 
 from .types import fdfield_t, fdfield_updater_t
 
@@ -61,9 +61,12 @@ def deriv_back(
     return derivs
 
 
+TT = TypeVar('TT', bound='NDArray[floating | complexfloating]')
+
+
 def curl_forward(
         dx_e: Sequence[NDArray[floating]] | None = None,
-        ) -> fdfield_updater_t:
+        ) -> Callable[[TT], TT]:
     r"""
     Curl operator for use with the E field.
 
@@ -77,7 +80,7 @@ def curl_forward(
     """
     Dx, Dy, Dz = deriv_forward(dx_e)
 
-    def ce_fun(e: fdfield_t) -> fdfield_t:
+    def ce_fun(e: TT) -> TT:
         output = numpy.empty_like(e)
         output[0] = Dy(e[2])
         output[1] = Dz(e[0])
@@ -92,7 +95,7 @@ def curl_forward(
 
 def curl_back(
         dx_h: Sequence[NDArray[floating]] | None = None,
-        ) -> fdfield_updater_t:
+        ) -> Callable[[TT], TT]:
     r"""
     Create a function which takes the backward curl of a field.
 
@@ -106,7 +109,7 @@ def curl_back(
     """
     Dx, Dy, Dz = deriv_back(dx_h)
 
-    def ch_fun(h: fdfield_t) -> fdfield_t:
+    def ch_fun(h: TT) -> TT:
         output = numpy.empty_like(h)
         output[0] = Dy(h[2])
         output[1] = Dz(h[0])
diff --git a/meanas/fdtd/pml.py b/meanas/fdtd/pml.py
index 9c3aec5..7678808 100644
--- a/meanas/fdtd/pml.py
+++ b/meanas/fdtd/pml.py
@@ -185,7 +185,7 @@ def updates_with_cpml(
     def update_H(
             e: fdfield_t,
             h: fdfield_t,
-            mu: fdfield_t = numpy.ones(3),
+            mu: fdfield_t | tuple[int, int, int] = (1, 1, 1),
             ) -> None:
         dyEx = Dfy(e[0])
         dzEx = Dfz(e[0])