diff --git a/QtPyLoT.py b/QtPyLoT.py
index cc4416c2..1ff21462 100755
--- a/QtPyLoT.py
+++ b/QtPyLoT.py
@@ -998,9 +998,16 @@ class MainWindow(QMainWindow):
                 w0, fc = calcsourcespec(wf, onset, fninv, self.inputs.get('vp'), dist,
                                         a.azimuth, a.takeoff_angle,
                                         self.inputs.get('Qp'), 0)
-                stat_mags = calcMoMw(wf, w0, 2700., 3000., dist, fninv)
-                mags[station] = stat_mags
+                if w0 is None or fc is None:
+                    continue
+                station_mag = calcMoMw(wf, w0, 2700., 3000., dist, fninv)
+                mags[station] = station_mag
             mag = np.median([M[1] for M in mags.values()])
+            # give some information on the processing
+            print('number of stations used: {0}\n'.format(len(mags.values())))
+            print('stations used:\n')
+            for s in mags.keys(): print('\t{0}'.format(s))
+
             return Magnitude(mag=mag, magnitude_type='Mw')
         else:
             return None