Hi, I can successfully use ZipArchive like the following -=-=- zip := ZipArchive new. { 'file1.txt'. 'file2.txt'. 'file3.txt' } do: [ :eachFile | | member | member := zip addString: eachFile, ' contents' as: eachFile. member desiredCompressionMethod: ZipArchive compressionDeflated ]. file := FileLocator temp / 'archive.zip'. zip writeTo: file writeStream. file. -=-=- What I should do to make it work while using FileSystem memory? -=-=- zip := ZipArchive new. { 'file1.txt'. 'file2.txt'. 'file3.txt' } do: [ :eachFile | | member | member := zip addString: eachFile, ' contents' as: eachFile. member desiredCompressionMethod: ZipArchive compressionDeflated ]. fileSystem := FileSystem memory. file := fileSystem root / 'archive.zip'. file writeStreamDo: [ :stream | zip writeTo: stream ]. -=-=- There is "Improper store into indexable objectâ as it tries to store a number in ByteString. Thanks! Juraj