I'm not sure the replacement of visitNumberDescription: aDescription | contents | contents := self contents. contents isEmpty ifTrue: [ MAReadError signal ]. (contents occurrencesOf: $-) > 1 ifTrue: [ MAReadError signal ]. (contents indexOf: $-) > 1 ifTrue: [ MAReadError signal ]. (contents occurrencesOf: $.) > 1 ifTrue: [ MAReadError signal ]. (contents allSatisfy: [ :each | '+-0123456789.eE' includes: each ]) ifFalse: [ MAReadError signal ]. super visitNumberDescription: aDescription by visitNumberDescription: aDescription | isContentsValid | isContentsValid := NumberParser isNumber: self contents. isContentsValid ifFalse: [ MAReadError signal ]. super visitNumberDescription: aDescription works cross-platform. There are two 455s, and 456 misses changes from both. Merged in 457 Stephan