diff --git a/tofu/geom/_GG.pyx b/tofu/geom/_GG.pyx
index 7143e078f..e2ce85d88 100644
--- a/tofu/geom/_GG.pyx
+++ b/tofu/geom/_GG.pyx
@@ -2985,16 +2985,16 @@ def LOS_calc_signal(func, double[:,::1] ray_orig, double[:,::1] ray_vdir, res,
             val_2d = func(pts, t=t, vect=-usbis, **fkwdargs)
         else:
             val_2d = func(pts, t=t, **fkwdargs)
+
         # Integrate
         if n_imode == 0:  # "sum" integration mode
             # .. integrating function ..........................................
-            for ii in range(nlos):
-                if ii > 0:
-                    sig[:,ii] = np.sum(val_2d[:, ind_arr[ii-1]:ind_arr[ii]],
-                                axis=-1) * reseff_arr[ii]
-                else:
-                    sig[:,0] = np.sum(val_2d[:, 0:ind_arr[0]],
-                                axis=-1) * reseff_arr[0]
+            reseffs = np.copy(np.asarray(<double[:nlos]>reseff_arr))
+            indices = np.copy(np.asarray(<long[:nlos-1]>ind_arr).astype(int))
+            sig = np.asfortranarray(np.add.reduceat(val_2d,
+                                                    np.r_[0, indices],
+                                                    axis=-1)
+                                    * reseffs[None, :])
             # Cleaning up...
             free(coeff_ptr[0])
             free(coeff_ptr)