diff --git a/Doc/c-api/long.rst b/Doc/c-api/long.rst
--- a/Doc/c-api/long.rst
+++ b/Doc/c-api/long.rst
@@ -78,25 +78,27 @@ All integers are implemented as "long" i
 
    Return a new :c:type:`PyLongObject` object from the integer part of *v*, or
    *NULL* on failure.
 
 
 .. c:function:: PyObject* PyLong_FromString(char *str, char **pend, int base)
 
    Return a new :c:type:`PyLongObject` based on the string value in *str*, which
-   is interpreted according to the radix in *base*.  If *pend* is non-*NULL*,
-   *\*pend* will point to the first character in *str* which follows the
-   representation of the number.  If *base* is ``0``, the radix will be
-   determined based on the leading characters of *str*: if *str* starts with
-   ``'0x'`` or ``'0X'``, radix 16 will be used; if *str* starts with ``'0o'`` or
-   ``'0O'``, radix 8 will be used; if *str* starts with ``'0b'`` or ``'0B'``,
-   radix 2 will be used; otherwise radix 10 will be used.  If *base* is not
-   ``0``, it must be between ``2`` and ``36``, inclusive.  Leading spaces are
-   ignored.  If there are no digits, :exc:`ValueError` will be raised.
+   is interpreted according to the radix in *base*.  If *base* is ``0``, the
+   radix will be determined based on the leading characters of *str*: if *str*
+   starts with ``'0x'`` or ``'0X'``, radix 16 will be used; if *str* starts with
+   ``'0o'`` or ``'0O'``, radix 8 will be used; if *str* starts with ``'0b'`` or
+   ``'0B'``, radix 2 will be used; otherwise radix 10 will be used.  If *base*
+   is not ``0``, it must be between ``2`` and ``36``, inclusive.
+
+   Leading spaces are ignored, and the representation of the number  must be
+   terminted by a null byte.  If *pend* is non-*NULL*, then *\*pend* will
+   point to the location of the terminating null byte.  If there are no
+   digits, :exc:`ValueError` will be raised.
 
 
 .. c:function:: PyObject* PyLong_FromUnicode(Py_UNICODE *u, Py_ssize_t length, int base)
 
    Convert a sequence of Unicode digits to a Python integer value.  The Unicode
    string is first encoded to a byte string using :c:func:`PyUnicode_EncodeDecimal`
    and then converted using :c:func:`PyLong_FromString`.