The error message comes from Undefined Behaviour Sanitizer, which was added to newer versions of GCC and Clang. Currently I am compiling with./configure --with-pydebug CC="gcc -fsanitize=undefined -fno-sanitize=alignment -fno-sanitize=shift"https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#index-fsanitize_003dundefined-962I thought it is worth adding a test for the impossible __length_hint__() value. Since the test iterator returns no elements, there will not be a MemoryError, but if overflow detection is enabled (such as UB Sanitizer or -ftrapv), it is guaranteed to exercise the overflow path and would be detected.