@@ -384,7 +384,7 @@ def _vectorized_make_sparse(subgraphs, hams, long [:] norbs, long [:] orb_offset

     cdef long i, j, k, m, N, M, P, to_off, from_off,\

               ta, fa, to_norbs, from_norbs

-    cdef long [:] ts_offs, fs_offs

+    cdef const long [:] ts_offs, fs_offs

     cdef complex [:, :, :] h

     m = 0

@@ -428,7 +428,7 @@ def _vectorized_make_dense(subgraphs, hams, long [:] norbs, long [:] orb_offsets

     cdef long i, j, k, N, M, P, to_off, from_off,\

               ta, fa, to_norbs, from_norbs

-    cdef long [:] ts_offs, fs_offs

+    cdef const long [:] ts_offs, fs_offs

     cdef complex [:, :, :] h

     # This outer loop zip() is pure Python, but that's ok, as it

@@ -2485,6 +2485,7 @@ def _make_onsite_terms(builder, sites, site_offsets, term_offset):

     tmp = []

     for (_, which), s in zip(onsite_to_term_nr, onsite_subgraphs):

         s = s - site_offsets[which]

+        s.flags.writeable = False

         tmp.append(((which, which), (s, s)))

     onsite_subgraphs = tmp

     # onsite_term_errors[i] contains an exception if the corresponding

@@ -2593,7 +2594,9 @@ def _make_hopping_terms(builder, graph, sites, site_offsets, cell_size, term_off

         # Transpose to get a pair of arrays rather than array of pairs

         # We use the fact that the underlying array is stored in

         # array-of-pairs order to search through it in 'hamiltonian'.

-        tmp.append(((tail_which, head_which), (h - start).transpose()))

+        pairs = (h - start).transpose()

+        pairs.flags.writeable = False

+        tmp.append(((tail_which, head_which), pairs))

     hopping_subgraphs = tmp

     # hopping_term_errors[i] contains an exception if the corresponding

     # term has a value function with an illegal signature. We only raise

@@ -471,8 +471,8 @@ def _vectorized_make_onsite_terms(syst, where):

     ret = []

     for term_id, which in terms.items():

         term = syst.terms[term_id]

-        ((term_sa, _), (term_sites, _)) = syst.subgraphs[term.subgraph]

-        term_sites += site_offsets[term_sa]

+        ((term_sa, _), (term_site_offsets, _)) = syst.subgraphs[term.subgraph]

+        term_sites = site_offsets[term_sa] + term_site_offsets

         which = np.asarray(which, dtype=gint_dtype)

         sites = _select(where, which).reshape(-1)

         selector = np.searchsorted(term_sites, sites)