Hi, This small change: https://pharo.fogbugz.com/f/cases/15436 improves the code generated by Slots when using the default “reflective write” (instead of generating their own optimised code like InstanceVariableSlots). The helper method #writeToSlot:of: in Object was just needed as the arguments where in the wrong oder on the stack. We can use writeSlot:value: by generating code like this: emitStore: aMethodBuilder | tempName | tempName := Object new. aMethodBuilder addTemp: tempName; storeTemp: tempName; popTop; pushReceiver; pushLiteral: self; pushTemp: tempName; send: #writeSlot:value: For what needs to be done, see https://trello.com/b/d59lgZFB/slots Marcus