diff --git a/site_ansto/instrument/bilby/config/chopper/chopper.tcl b/site_ansto/instrument/bilby/config/chopper/chopper.tcl
index ae30efe2..80394e93 100644
--- a/site_ansto/instrument/bilby/config/chopper/chopper.tcl
+++ b/site_ansto/instrument/bilby/config/chopper/chopper.tcl
@@ -26,7 +26,7 @@ if {$sim_mode == false} {
       if {$::chopper::t0_chopper_id_simvar < 1 || $::chopper::t0_chopper_id_simvar > 4} {
         return -code error "Your simulated chopper returned an error"
       } else {
-        return t0_chopper_id = $::chopper::t0_chopper_id_simvar
+        return "t0_chopper_id = $::chopper::t0_chopper_id_simvar"
       }
     } else {
       set ::chopper::t0_chopper_id_simvar $args
@@ -35,4 +35,4 @@ if {$sim_mode == false} {
 }
 sicslist setatt t0_chopper_id klass NXdisk_chopper
 sicslist setatt t0_chopper_id long_name t0_chopper_id
-sicslist setatt t0_chopper_id mutable false
+sicslist setatt t0_chopper_id mutable true