--- a/src/ov-bool-sparse.cc
+++ b/src/ov-bool-sparse.cc
@@ -699,20 +699,20 @@
 mxArray *
 octave_sparse_bool_matrix::as_mxArray (void) const
 {
-  int nz = nzmax ();
+  mwSize nz = nzmax ();
   mxArray *retval = new mxArray (mxLOGICAL_CLASS, rows (), columns (), 
 				 nz, mxREAL);
   bool *pr = static_cast<bool *> (retval->get_data ());
-  int *ir = retval->get_ir ();
-  int *jc = retval->get_jc ();
+  mwIndex *ir = retval->get_ir ();
+  mwIndex *jc = retval->get_jc ();
 
-  for (int i = 0; i < nz; i++)
+  for (mwIndex i = 0; i < nz; i++)
     {
       pr[i] = matrix.data(i);
       ir[i] = matrix.ridx(i);
     }
 
-  for (int i = 0; i < columns () + 1; i++)
+  for (mwIndex i = 0; i < columns () + 1; i++)
     jc[i] = matrix.cidx(i);
 
   return retval;