@@ -2509,7 +2509,7 @@ def _make_onsite_terms(builder, sites, site_offsets, term_offset):

     _onsite_term_by_site_id = np.array(_onsite_term_by_site_id)

     return (onsite_subgraphs, onsite_terms, onsite_term_values,

-            onsite_term_parameters, onsite_term_errors, _onsite_term_by_site_id)

+            onsite_term_errors, _onsite_term_by_site_id)

 def _make_hopping_terms(builder, graph, sites, site_offsets, cell_size, term_offset):

@@ -2619,8 +2619,7 @@ def _make_hopping_terms(builder, graph, sites, site_offsets, cell_size, term_off

     _hopping_term_by_edge_id = np.array(_hopping_term_by_edge_id)

     return (hopping_subgraphs, hopping_terms, hopping_term_values,

-            hopping_term_parameters, hopping_term_errors,

-            _hopping_term_by_edge_id)

+            hopping_term_errors, _hopping_term_by_edge_id)

 class FiniteVectorizedSystem(_VectorizedFinalizedBuilderMixin, system.FiniteVectorizedSystem):

@@ -2667,12 +2666,11 @@ class FiniteVectorizedSystem(_VectorizedFinalizedBuilderMixin, system.FiniteVect

         site_offsets = np.cumsum([0] + [len(arr) for arr in site_arrays])

         (onsite_subgraphs, onsite_terms, onsite_term_values,

-         onsite_term_parameters, onsite_term_errors, _onsite_term_by_site_id) =\

+         onsite_term_errors, _onsite_term_by_site_id) =\

             _make_onsite_terms(builder, sites, site_offsets, term_offset=0)

         (hopping_subgraphs, hopping_terms, hopping_term_values,

-         hopping_term_parameters, hopping_term_errors,

-         _hopping_term_by_edge_id) =\

+         hopping_term_errors, _hopping_term_by_edge_id) =\

             _make_hopping_terms(builder, graph, sites, site_offsets,

                                 len(sites), term_offset=len(onsite_terms))

@@ -2684,9 +2682,9 @@ class FiniteVectorizedSystem(_VectorizedFinalizedBuilderMixin, system.FiniteVect

         # Construct system parameters

         parameters = set()

-        for params in chain(onsite_term_parameters, hopping_term_parameters):

-            if params is not None:

-                parameters.update(params)

+        for term in terms:

+            if term.parameters is not None:

+                parameters.update(term.parameters)

         parameters = frozenset(parameters)

         self.site_arrays = site_arrays

@@ -2979,12 +2977,11 @@ class InfiniteVectorizedSystem(_VectorizedFinalizedBuilderMixin, system.Infinite

         site_offsets = np.cumsum([0] + [len(arr) for arr in site_arrays])

         (onsite_subgraphs, onsite_terms, onsite_term_values,

-         onsite_term_parameters, onsite_term_errors, _onsite_term_by_site_id) =\

+         onsite_term_errors, _onsite_term_by_site_id) =\

             _make_onsite_terms(builder, sites, site_offsets, term_offset=0)

         (hopping_subgraphs, hopping_terms, hopping_term_values,

-         hopping_term_parameters, hopping_term_errors,

-         _hopping_term_by_edge_id) =\

+         hopping_term_errors, _hopping_term_by_edge_id) =\

             _make_hopping_terms(builder, graph, sites, site_offsets,

                                 cell_size, term_offset=len(onsite_terms))

@@ -2996,9 +2993,9 @@ class InfiniteVectorizedSystem(_VectorizedFinalizedBuilderMixin, system.Infinite

         # Construct system parameters

         parameters = set()

-        for params in chain(onsite_term_parameters, hopping_term_parameters):

-            if params is not None:

-                parameters.update(params)

+        for term in terms:

+            if term.parameters is not None:

+                parameters.update(term.parameters)

         parameters = frozenset(parameters)

         self.site_arrays = site_arrays

@@ -1547,6 +1547,25 @@ def test_argument_passing(vectorize):

         expected_hamiltonian(**params)

     )

+@pytest.mark.parametrize("vectorize", [False, True])

+def test_invalid_value_functions(vectorize):

+

+    invalid_value_functions = [

+        lambda _, *args: 1,  # uses *args

+        lambda _, **kwargs: 1,  # uses **kwargs

+        lambda _, d=10: 1,  # has default arguments

+        lambda _, *, d: 1  # has keyword-only parameters

+    ]

+

+    lat = kwant.lattice.chain(norbs=1)

+

+    for f in invalid_value_functions:

+        syst = builder.Builder(vectorize=vectorize)

+        syst[lat(0)] = f

+        syst = syst.finalized()

+        with pytest.raises(ValueError):

+            syst.hamiltonian_submatrix(params=dict(d=1))

+

 def test_parameter_substitution():