I think those lines are the problem:"0 >= start, fail"cogit CmpCq: (objectMemory integerObjectOf: 0) R: startReg.jumpOutOfBounds1 := cogit JumpLess: 0."0 >= replStart, fail"cogit CmpCq: (objectMemory integerObjectOf: 0) R: repStartReg.jumpOutOfBounds2 := cogit JumpLess: 0.If this is equal if should jump out of bounds.On Sun, Nov 26, 2017 at 9:53 PM, Clément Bera <bera.clement@gmail.com> wrote:Bug seems to be with underflow access on replacement array:(1 to: 10) collect: [:i| ['123456789' replaceFrom: 1 to: 4 with: 'abcdefgh' startingAt: 0] on: Error do: ['error']]#('error' ' abc56789' ' abc56789' ' abc56789' ' abc56789' ' abc56789' ' abc56789' ' abc56789' ' abc56789' ' abc56789').Same thing on arrays since this is common code...Generated code looks ok... I need to look again I may have inverted some branches.On Sun, Nov 26, 2017 at 9:37 PM, Clément Bera <bera.clement@gmail.com> wrote:Ok I have a look.This is on byte objects...On Sun, Nov 26, 2017 at 9:07 PM, Nicolas Cellier <nicolas.cellier.aka.nice@gmail.com > wrote:the testTextReplacement3 now fails randomly.It sometimes omit to signal an Error...--Clément BéraPharo consortium engineerBâtiment B 40, avenue Halley 59650 Villeneuve d'Ascq--Clément BéraPharo consortium engineerBâtiment B 40, avenue Halley 59650 Villeneuve d'Ascq--Clément BéraPharo consortium engineerBâtiment B 40, avenue Halley 59650 Villeneuve d'Ascq