diff --git a/Code/Mantid/scripts/Inelastic/DirectEnergyConversion.py b/Code/Mantid/scripts/Inelastic/DirectEnergyConversion.py
index d567d69efb78..ef5fbef91df6 100644
--- a/Code/Mantid/scripts/Inelastic/DirectEnergyConversion.py
+++ b/Code/Mantid/scripts/Inelastic/DirectEnergyConversion.py
@@ -622,7 +622,9 @@ def normalise(self, data_ws, result_name, method, range_offset=0.0,mon_number=No
 
             monWS_name = data_ws.getName()+'_monitors'
             if monWS_name in mtd:
-                NormaliseToMonitor(InputWorkspace=data_ws, OutputWorkspace=result_name, MonitorWorkspace=monWS_name, 
+                mon_ws = mtd[monWS_name];
+                mon_index = mon_ws.getIndexFromSpectrumNumber(mon_spectr_num);
+                NormaliseToMonitor(InputWorkspace=data_ws, OutputWorkspace=result_name, MonitorWorkspace=mon_ws, MonitorWorkspaceIndex=mon_index,
                                    IntegrationRangeMin=float(str(range_min)), IntegrationRangeMax=float(str(range_max)),IncludePartialBins=True)
             else:
                 NormaliseToMonitor(InputWorkspace=data_ws, OutputWorkspace=result_name, MonitorSpectrum=mon_spectr_num,