diff --git a/kwant/graph/c_slicer/partitioner.cc b/kwant/graph/c_slicer/partitioner.cc
index 394cb62702fadd5258e9a3ffcde0a26cde373103..ea74bddb7fb4f5b213e12310b190ea1ccab42d7b 100644
--- a/kwant/graph/c_slicer/partitioner.cc
+++ b/kwant/graph/c_slicer/partitioner.cc
@@ -116,7 +116,7 @@ void Partitioner::bisectFirst(std::vector<int> &_left, std::vector<int> &_right,
   if(slices<2) return;
 
   //Find the maximum number of edges (needed or Fiduccia-Mattheyses)
-  int max_edges=0;
+  size_t max_edges=0;
 
   for(size_t ivertex=0; ivertex < parts[0].size(); ivertex++) {
     if(graph.getEdges(parts[0][ivertex]).size() > max_edges) {
diff --git a/kwant/graph/utils.pyx b/kwant/graph/utils.pyx
index 678424ccd8d88f351a71ddf29a0ddb064950a1fe..33ffff6f3017cc83422cf7b666e561d123f99393 100644
--- a/kwant/graph/utils.pyx
+++ b/kwant/graph/utils.pyx
@@ -216,7 +216,7 @@ def induced_subgraph(CGraph gr, select,
 
     cdef np.ndarray[gint, ndim=1] indextab
     cdef CGraph_malloc subgr
-    cdef np.ndarray[gint, ndim=1] sub_edge_weights
+    cdef np.ndarray[gint, ndim=1] sub_edge_weights = None
     cdef gint sub_num_nodes, sub_num_edges
     cdef gint i, iedge, edge_count
 
diff --git a/kwant/operator.pyx b/kwant/operator.pyx
index 5e8fbd3d8c83a1549ead341904ea61eedd1708bd..1dd134933bbde396f91ccd559133b1b2a4e11884 100644
--- a/kwant/operator.pyx
+++ b/kwant/operator.pyx
@@ -684,7 +684,10 @@ cdef class Density(_LocalOperator):
             data = np.asarray(self.onsite).flatten()
             data = np.resize(data, [len(data) * n_blocks])
         else:
-            onsite_matrix = self._bound_onsite or self._eval_onsites(args)
+            if self._bound_onsite is not None:
+                onsite_matrix = self._bound_onsite
+            else:
+                onsite_matrix = self._eval_onsites(args)
             data = onsite_matrix.data
             offsets = np.asarray(onsite_matrix.block_offsets)
             shapes = np.asarray(onsite_matrix.block_shapes)