The doctest engine uses a regexp which contains subpattern which now considered as illegal be the regexp engine (due to unlucky coincidence MAXREPEAT == sys.maxsize on 32-bit platforms). We should rewrite the _simple() function in the re module to be more smart. But if this assumption is correct and this subpattern is really dangerous we should also rewrite a regular expression in the doctest module. In any case we should fix SubPattern.getwidth() so that the behavior on 32-bit and 64-bit platforms should be the same.