diff --git a/Framework/DataHandling/src/LoadBBY.cpp b/Framework/DataHandling/src/LoadBBY.cpp
index 5c670badbacd110171d22b117186b3d4f9f54c32..e117a87dd617cc5e692cc6004b882e83dfb34e31 100644
--- a/Framework/DataHandling/src/LoadBBY.cpp
+++ b/Framework/DataHandling/src/LoadBBY.cpp
@@ -405,6 +405,7 @@ void LoadBBY::exec() {
       createChildAlgorithm("LoadInstrument");
   loadInstrumentAlg->setProperty("Workspace", eventWS);
   loadInstrumentAlg->setPropertyValue("InstrumentName", "BILBY");
+  loadInstrumentAlg->setProperty("RewriteSpectraMap", false);
   loadInstrumentAlg->executeAsChildAlg();
 
   setProperty("OutputWorkspace", eventWS);
@@ -826,4 +827,4 @@ void BbyDetectorBankFactory::createAndAssign(size_t startIndex,
 }
 
 } // DataHandling
-} // Mantid
\ No newline at end of file
+} // Mantid
diff --git a/instrument/Bilby_Definition.xml b/instrument/Bilby_Definition.xml
index 81029ac258ae427777382b1c5f79f82a6478b94b..baa7b5eabc3295fd9b5a62f63f452d9a2aff8810 100644
--- a/instrument/Bilby_Definition.xml
+++ b/instrument/Bilby_Definition.xml
@@ -26,7 +26,7 @@
   <component name="Source" type="source">
     <location x="0.0" y="0.0" />
     <parameter name="z"> 
-      <logfile id="L1_chopper_value" eq="1*value"/>
+      <logfile id="L1_chopper_value" eq="-1*value"/>
     </parameter>
   </component>
   <type name="source" is="Source" />
@@ -503,4 +503,4 @@
    
   
 </instrument>
-  
\ No newline at end of file
+