Attached patch raises a ValueError if the current recursion depth is higher than the new "low-water mark". The low-water mark is the value computed by _Py_MakeEndRecCheck() in Py_LeaveRecursiveCall() to decide if we can reset the overflowed field of the thread state to 0. Example of error with the patch: $ ./python -c 'import sys; sys.setrecursionlimit(2)' Traceback (most recent call last): File "<string>", line 1, in <module> ValueError: cannot set recursion limit to 2: the minimum recursion limit is 1 at the recursion depth 1