diff --git a/mushroom/aims/gw.py b/mushroom/aims/gw.py
index 9a500e1..6b6e763 100644
--- a/mushroom/aims/gw.py
+++ b/mushroom/aims/gw.py
@@ -249,7 +249,10 @@ def set_sigc(n, s, kp, k, sigc):
         data_bands.append(data_band)
 
     if merge_band_kpoints:
-        data_bands = np.concatenate(data_bands, axis=2)
+        if len(data_bands) > 0:
+            data_bands = np.concatenate(data_bands, axis=2)
+        else:
+            data_bands = np.zeros((nomegas, nspins, 0, nstates))
 
     return omegas, state_low, data_kgrid, data_bands
 
diff --git a/scripts/m_aims_append_basis b/scripts/m_aims_append_basis
index 8a84e00..2a5f373 100755
--- a/scripts/m_aims_append_basis
+++ b/scripts/m_aims_append_basis
@@ -30,8 +30,9 @@ def m_aims_apppend_basis(control_file, directory, *elem, species_defaults=None):
     if len(regions) > 1:
         print("Replacing existing basis information in control file {}".format(control_file))
     sl = readlines_species_defaults(directory, *elem, species_defaults=species_defaults)
+    ctrl_new = "".join(gl) + sl
     with open(control_file, 'w') as h:
-        print("".join(gl + sl), file=h)
+        print(ctrl_new, file=h)
 
 
 if __name__ == '__main__':