diff --git a/libeos/file_reader.py b/libeos/file_reader.py
index d9850c0..a188541 100644
--- a/libeos/file_reader.py
+++ b/libeos/file_reader.py
@@ -249,9 +249,7 @@ class AmorData:
 
     def merge_frames(self):
         total_offset = self.tofCut+self.tau*self.config.chopperPhaseOffset/180.
-        #if nb_helpers:
-        if False:
-            # TODO: this routine seems to ignore total_offset
+        if nb_helpers:
             self.tof_e = nb_helpers.merge_frames(self.tof_e, self.tofCut, self.tau, total_offset)
         else:
             self.tof_e = np.remainder(self.tof_e-(self.tofCut-self.tau), self.tau)+total_offset  # tof shifted to 1 frame
diff --git a/libeos/nb_helpers.py b/libeos/nb_helpers.py
index 8f69824..52efc95 100644
--- a/libeos/nb_helpers.py
+++ b/libeos/nb_helpers.py
@@ -9,7 +9,7 @@ def merge_frames(tof_e, tofCut, tau, total_offset):
     dt = (tofCut-tau)
     for ti in nb.prange(tof_e.shape[0]):
         tof_e_out[ti] = ((tof_e[ti]-dt)%tau)+total_offset  # tof shifted to 1 frame
-    return tof_e
+    return tof_e_out
 
 @nb.jit(nb.float64[:](nb.float64[:], nb.uint64[:], nb.float64[:]),
         nopython=True, parallel=True, cache=True)
@@ -62,4 +62,4 @@ def calculate_derived_properties_focussing(tof_e, detXdist_e, delta_e, mask_e,
         mask_e_out[i] = mask_e[i] & ((lmin<=lamda_e[i]) & (lamda_e[i]<=lmax))
         alphaF_e[i] = nu-mu+delta_e[i]
         qz_e[i] = 4*np.pi*np.sin(np.deg2rad(alphaF_e[i]))/lamda_e[i]
-    return lamda_e, qz_e, mask_e
\ No newline at end of file
+    return lamda_e, qz_e, mask_e