diff --git a/tardis/montecarlo/src/cmontecarlo.c b/tardis/montecarlo/src/cmontecarlo.c
index 357a4c32506..714cb284aa2 100644
--- a/tardis/montecarlo/src/cmontecarlo.c
+++ b/tardis/montecarlo/src/cmontecarlo.c
@@ -137,67 +137,62 @@ void calculate_chi_bf(rpacket_t * packet, storage_model_t * storage)
   rpacket_set_chi_boundfree(packet, bf_helper * doppler_factor);
 }
 
-double
+void
 compute_distance2boundary (rpacket_t * packet, const storage_model_t * storage)
 {
   double r = rpacket_get_r (packet);
   double mu = rpacket_get_mu (packet);
   double r_outer = storage->r_outer[rpacket_get_current_shell_id (packet)];
   double r_inner = storage->r_inner[rpacket_get_current_shell_id (packet)];
-  double d_outer =
-    sqrt (r_outer * r_outer + ((mu * mu - 1.0) * r * r)) - (r * mu);
-  double d_inner;
+  double check, distance;
   if (rpacket_get_recently_crossed_boundary (packet) == 1)
     {
       rpacket_set_next_shell_id (packet, 1);
-      return d_outer;
+      distance = sqrt (r_outer * r_outer + ((mu * mu - 1.0) * r * r)) - (r * mu);
+    }
+  else if (mu > 0.0)
+    { // direction outward
+      rpacket_set_next_shell_id (packet, 1);
+      distance = sqrt (r_outer * r_outer + ((mu * mu - 1.0) * r * r)) - (r * mu);
     }
   else
-    {
-      double check = r_inner * r_inner + (r * r * (mu * mu - 1.0));
-      if (check < 0.0)
-        {
-          rpacket_set_next_shell_id (packet, 1);
-          return d_outer;
+    { // going inward
+      if ( (check = r_inner * r_inner + (r * r * (mu * mu - 1.0)) )>= 0.0)
+        { // hit inner boundary
+          rpacket_set_next_shell_id (packet, -1);
+          distance = - r * mu - sqrt (check);
         }
       else
-        {
-          d_inner = mu < 0.0 ? -r * mu - sqrt (check) : MISS_DISTANCE;
+        { // miss inner boundary
+          rpacket_set_next_shell_id (packet, 1);
+          distance = sqrt (r_outer * r_outer + ((mu * mu - 1.0) * r * r)) - (r * mu);
         }
     }
-  if (d_inner < d_outer)
-    {
-      rpacket_set_next_shell_id (packet, -1);
-      return d_inner;
-    }
-  else
-    {
-      rpacket_set_next_shell_id (packet, 1);
-      return d_outer;
-    }
+  rpacket_set_d_boundary (packet, distance);
 }
 
 tardis_error_t
-compute_distance2line (const rpacket_t * packet, const storage_model_t * storage,
-                       double *result)
+compute_distance2line (rpacket_t * packet, const storage_model_t * storage)
 {
-  tardis_error_t ret_val = TARDIS_ERROR_OK;
-  if (rpacket_get_last_line (packet))
-    {
-      *result = MISS_DISTANCE;
-    }
-  else
+  if (!rpacket_get_last_line (packet))
     {
       double r = rpacket_get_r (packet);
       double mu = rpacket_get_mu (packet);
       double nu = rpacket_get_nu (packet);
       double nu_line = rpacket_get_nu_line (packet);
+      double distance, nu_diff;
       double t_exp = storage->time_explosion;
       double inverse_t_exp = storage->inverse_time_explosion;
       int64_t cur_zone_id = rpacket_get_current_shell_id (packet);
       double doppler_factor = 1.0 - mu * r * inverse_t_exp * INVERSE_C;
       double comov_nu = nu * doppler_factor;
-      if (comov_nu < nu_line)
+      if ( (nu_diff = comov_nu - nu_line) >= 0)
+        {
+          distance = (nu_diff / nu) * C * t_exp;
+          rpacket_set_d_line (packet, distance);
+          return TARDIS_ERROR_OK;
+        }
+      else
         {
           if (rpacket_get_next_line_id (packet) == storage->no_of_lines - 1)
             {
@@ -232,14 +227,14 @@ compute_distance2line (const rpacket_t * packet, const storage_model_t * storage
           fprintf (stderr, "nu = %f\n", nu);
           fprintf (stderr, "doppler_factor = %f\n", doppler_factor);
           fprintf (stderr, "cur_zone_id = %" PRIi64 "\n", cur_zone_id);
-          ret_val = TARDIS_ERROR_COMOV_NU_LESS_THAN_NU_LINE;
-        }
-      else
-        {
-          *result = ((comov_nu - nu_line) / nu) * C * t_exp;
+          return TARDIS_ERROR_COMOV_NU_LESS_THAN_NU_LINE;
         }
     }
-  return ret_val;
+  else
+    {
+      rpacket_set_d_line (packet, MISS_DISTANCE);
+      return TARDIS_ERROR_OK;
+    }
 }
 
 void
@@ -712,12 +707,9 @@ montecarlo_compute_distances (rpacket_t * packet, storage_model_t * storage)
     }
   else
     {
-      rpacket_set_d_boundary (packet,
-                              compute_distance2boundary (packet, storage));
-      double d_line;
-      compute_distance2line (packet, storage, &d_line);
+      compute_distance2boundary(packet, storage);
+      compute_distance2line (packet, storage);
       // FIXME MR: return status of compute_distance2line() is ignored
-      rpacket_set_d_line (packet, d_line);
       compute_distance2continuum (packet, storage);
     }
 }
diff --git a/tardis/montecarlo/src/cmontecarlo.h b/tardis/montecarlo/src/cmontecarlo.h
index b22b658e813..8f2b5676671 100644
--- a/tardis/montecarlo/src/cmontecarlo.h
+++ b/tardis/montecarlo/src/cmontecarlo.h
@@ -33,7 +33,7 @@ double rpacket_doppler_factor(const rpacket_t *packet, const storage_model_t *st
  *
  * @return distance to shell boundary
  */
-double compute_distance2boundary (rpacket_t * packet,
+void compute_distance2boundary (rpacket_t * packet,
                                   const storage_model_t * storage);
 
 /** Calculate the distance the packet has to travel until it redshifts to the first spectral line.
@@ -43,9 +43,8 @@ double compute_distance2boundary (rpacket_t * packet,
  *
  * @return distance to the next spectral line
  */
-tardis_error_t compute_distance2line (const rpacket_t * packet,
-                                      const storage_model_t * storage,
-                                      double *result);
+tardis_error_t compute_distance2line (rpacket_t * packet,
+                                      const storage_model_t * storage);
 
 /** Calculate the distance to the next continuum event, which can be a Thomson scattering, bound-free absorption or
   free-free transition.
diff --git a/tardis/montecarlo/src/test_cmontecarlo.c b/tardis/montecarlo/src/test_cmontecarlo.c
index 80fa06fb190..6657c14392c 100644
--- a/tardis/montecarlo/src/test_cmontecarlo.c
+++ b/tardis/montecarlo/src/test_cmontecarlo.c
@@ -220,10 +220,10 @@ test_compute_distance2boundary(void){
         storage_model_t sm;
         init_rpacket(&rp);
         init_storage_model(&sm);
-        double D_BOUNDARY = compute_distance2boundary(&rp, &sm);
-	rpacket_set_d_boundary(&rp, D_BOUNDARY);
+        compute_distance2boundary(&rp, &sm);
+        double D_BOUNDARY = rpacket_get_d_boundary(&rp);
         dealloc_storage_model(&sm);
-	return D_BOUNDARY;
+        return D_BOUNDARY;
 }
 double
 test_compute_distance2line(void){
@@ -231,12 +231,11 @@ test_compute_distance2line(void){
         storage_model_t sm;
         init_rpacket(&rp);
         init_storage_model(&sm);
-	double D_LINE;
         // FIXME MR: return status of compute_distance2line() is ignored
-	compute_distance2line(&rp, &sm, &D_LINE);
-	rpacket_set_d_line(&rp, D_LINE);
+        compute_distance2line(&rp, &sm);
+        double D_LINE = rpacket_get_d_line(&rp);
         dealloc_storage_model(&sm);
-	return D_LINE;
+        return D_LINE;
 }
 
 double
@@ -279,17 +278,12 @@ test_increment_j_blue_estimator(void){
         storage_model_t sm;
         init_rpacket(&rp);
         init_storage_model(&sm);
-	int64_t j_blue_idx = 0;
-        double D_BOUNDARY = compute_distance2boundary(&rp, &sm);
-        rpacket_set_d_boundary(&rp, D_BOUNDARY);
-        double D_LINE;
-        // FIXME MR: return status of compute_distance2line() is ignored
-        compute_distance2line(&rp, &sm, &D_LINE);
-        rpacket_set_d_line(&rp, D_LINE);
+        int64_t j_blue_idx = 0;
+        compute_distance2line(&rp, &sm);
         move_packet(&rp, &sm, 1e13);
-	double d_line = rpacket_get_d_line(&rp);
-	increment_j_blue_estimator(&rp, &sm, d_line, j_blue_idx);
-	double res = sm.line_lists_j_blues[j_blue_idx];
+        double d_line = rpacket_get_d_line(&rp);
+        increment_j_blue_estimator(&rp, &sm, d_line, j_blue_idx);
+        double res = sm.line_lists_j_blues[j_blue_idx];
         dealloc_storage_model(&sm);
         return res;
 }
@@ -379,12 +373,7 @@ test_calculate_chi_bf(void){
         rk_state mt_state;
         irandom(&mt_state);
         int64_t j_blue_idx = 0;
-        double D_BOUNDARY = compute_distance2boundary(&rp, &sm);
-        rpacket_set_d_boundary(&rp, D_BOUNDARY);
-        double D_LINE;
-        // FIXME MR: return status of compute_distance2line() is ignored
-        compute_distance2line(&rp, &sm, &D_LINE);
-        rpacket_set_d_line(&rp, D_LINE);
+        compute_distance2line(&rp, &sm);
         move_packet(&rp, &sm, 1e13);
         double d_line = rpacket_get_d_line(&rp);
         increment_j_blue_estimator(&rp, &sm, d_line, j_blue_idx);