Hello Rick, thank you. --pdump lets me build xemacs 21.5.16 without problems on Cygwin. I tried some different configuration options under Cygwin/WinXP and made following observations: (1) --debug=no --error-checking=none --pdump --use-kkcc build fine but resulted in a total crash of WinXP without bluescreen on loading files with xemac (reproducible total crash). Starting xemacs and loading plain text files worked fine, but in the moment I loaded an lisp or caml file the machine crashed. (1b) So I thought it would be --pdump or --use-kkcc, but changing these options resulted in OS-crash, too. (2) --debug=no --pdump --use-kkcc works fine, no errors; "stability" is achieved by error-checking (I think you made it the default because of that). Perhaps --pdump should be made default for Cygwin?