diff --git a/phi/field/_grid.py b/phi/field/_grid.py
index 5bd4c1700..794f4ebf1 100644
--- a/phi/field/_grid.py
+++ b/phi/field/_grid.py
@@ -518,10 +518,9 @@ def resolution_from_staggered_tensor(values: Tensor, extrapolation: Extrapolatio
 
 
 def _sample_function(f, elements: Geometry):
-    import inspect
+    from phi.math._functional import get_function_parameters
     try:
-        signature = inspect.signature(f)
-        params = dict(signature.parameters)
+        params = get_function_parameters(f)
         dims = elements.shape.get_size('vector')
         names_match = tuple(params.keys())[:dims] == elements.shape.get_item_names('vector')
         num_positional = 0
@@ -531,10 +530,10 @@ def _sample_function(f, elements: Geometry):
                 num_positional += 1
             if p.kind == 2:  # _ParameterKind.VAR_POSITIONAL
                 has_varargs = True
-        assert num_positional <= dims, f"Cannot sample {f.__name__}{signature} on physical space {elements.shape.get_item_names('vector')}"
+        assert num_positional <= dims, f"Cannot sample {f.__name__}({', '.join(tuple(params))}) on physical space {elements.shape.get_item_names('vector')}"
         pass_varargs = has_varargs or names_match or num_positional > 1 or num_positional == dims
         if num_positional > 1 and not has_varargs:
-            assert names_match, f"Positional arguments of {f.__name__}{signature} should match physical space {elements.shape.get_item_names('vector')}"
+            assert names_match, f"Positional arguments of {f.__name__}({', '.join(tuple(params))}) should match physical space {elements.shape.get_item_names('vector')}"
     except ValueError as err:  # signature not available for all functions
         pass_varargs = False
     if pass_varargs: