Hi folks Iâve been trying to load Fuel into Squeak 5 but canât because I get errors when loading Traits (they have not instance variables). The reason for this error seems to be that #instSize answers 2 for Traits when it should answer 0. The current implementation is: ^format bitAnd: 16rFFFF The comment in the 4.6 version says: " NOTE: This code supports the backward-compatible extension to 8 bits of instSize. When we revise the image format, it should become... ^ ((format bitShift: -1) bitAnd: 16rFF) - 1 Note also that every other method in this category will require 2 bits more of right shift after the change. â When I use that version in TraitBehaviour>>instSize in Squeak 5 I get 0 as expected and I can load Fuel without problems. Cheers, Max