--- a/compute.c
+++ b/compute.c
@@ -210,7 +210,7 @@
 
   Current_atom = atom_id;
 
-  if (!compute_neighbors(atom_id, &num_constraints)) return;
+  if (!compute_neighbors(atom_id, &num_constraints)) return -1;
 
   compute_planes(atom_id, num_constraints,constraints);
 
@@ -597,7 +597,7 @@
   */
   if (all_verts_in_sphere(rvertices, rvertices_count, sq_radius)) 
   { /* printf("atom_id %d all_in = TRUE \n", atom_id); */
-    return;
+    return -1;
   }
 
   for(i = 0; i < rfaces_count; i++)	       /* for each face    */
@@ -647,7 +647,7 @@
   if (DOTPROD3(diff, diff) < 1e-10)
   /* atom center lies in the feasible region, and so can be also
      taken to be the tes_origin - no more computations required */
-    return;
+    return -1;
 
   /* try computing the tes_origin as the average of all int_pts */
   VEC3_ZERO(temp_origin); count = 0;
--- a/tessel_concave.c
+++ b/tessel_concave.c
@@ -178,7 +178,7 @@
   if ((sq_side_len[0] < EPS) && 
       (sq_side_len[1] < EPS) && 
       (sq_side_len[2] < EPS)) 
-  { return;
+  { return -1;
   }
 
   /* evaluate which side of the plane the points lie wrt the probe center */
@@ -195,14 +195,14 @@
   max_len = FMAX((FMAX(sq_side_len[0], sq_side_len[1])), sq_side_len[2]);
   max_side = (max_len==sq_side_len[0])?0:((max_len==sq_side_len[1])? 1 : 2);
 
-  if (num_fine_points == 0) return;      /* all points are on the wrong side */
+  if (num_fine_points == 0) return -1;      /* all points are on the wrong side */
 
   if (max_len <= Max_Tess_Len_Sq)
   { /* sufficiently small so display but first check to see whether it
        intersects the plane or not and if so, clip it accordingly */
     if (num_fine_points == 3)
     { gen_tris(points[0], points[1], points[2]);
-      return;
+      return -1;
     }
     else if (num_fine_points == 1) /* two points are on the wrong side */
       i = (itemp[0] == 1)? 0 : ((itemp[1] == 1)? 1: 2);
@@ -305,7 +305,7 @@
       (sq_side_len[1] < EPS) && 
       (sq_side_len[2] < EPS)) 
   { 
-    return;
+    return -1;
   }
 
   if (max_len > Max_Tess_Len_Sq)
--- a/tessel_convex.c
+++ b/tessel_convex.c
@@ -74,7 +74,7 @@
      atoms[atom_id].center[Y], atoms[atom_id].center[Z], atoms[atom_id].radius);
     fflush(stderr);
     free(sph_side);
-    return;
+    return -1;
   }
 
   
--- a/tessel_torus.c
+++ b/tessel_torus.c
@@ -191,7 +191,7 @@
 
   if (j > n)
   { printf("gen_torus(): Too many torus verts %d (limit %d)\n",j, n);
-    return ;
+    return -1;
   }
   old_j = j;
 
@@ -202,7 +202,7 @@
     gen_linear_recurse(tor_pts[0][i],tor_pts[1][i],r[k],&j,fcenter,fradius,0);
     if (j > n)
     { printf("gen_torus(): Too many torus verts %d (limit %d)\n",j, n);
-      return ;
+      return -1;
     }
 
     for(m = 0; m < j-1; m++)
--- a/utils.c
+++ b/utils.c
@@ -91,7 +91,7 @@
   disc = radius*radius - DOTPROD3(EO, EO);
   if (FP_EQ_EPS(disc, 0, GP_EPS*GP_EPS))
   { VEC3_ASN_OP(int_point, =, ray_pt);
-    return;
+    return -1;
   }
 
   one_by_sq_dir_mag = 1.0/DOTPROD3(ray_dir, ray_dir);