diff --git a/Doc/c-api/long.rst b/Doc/c-api/long.rst
index f09abea7429f14..7650d98fdea421 100644
--- a/Doc/c-api/long.rst
+++ b/Doc/c-api/long.rst
@@ -685,7 +685,7 @@ Export API
       - ``1`` for most significant digit first
       - ``-1`` for least significant digit first
 
-   .. c:member:: int8_t endian
+   .. c:member:: int8_t digit_endianness
 
       Digit endianness:
 
@@ -772,19 +772,20 @@ The :c:type:`PyLongWriter` API can be used to import an integer.
 
    Create a :c:type:`PyLongWriter`.
 
-   On success, set *\*digits* and return a writer.
+   On success, allocate *\*digits* and return a writer.
    On error, set an exception and return ``NULL``.
 
    *negative* is ``1`` if the number is negative, or ``0`` otherwise.
 
    *ndigits* is the number of digits in the *digits* array. It must be
-   greater than or equal to 0.
+   greater than 0.
 
-   The caller can either initialize the array of digits *digits* and then call
-   :c:func:`PyLongWriter_Finish` to get a Python :class:`int`, or call
+   The caller can either initialize the array of digits *digits* and then
+   either call :c:func:`PyLongWriter_Finish` to get a Python :class:`int` or
    :c:func:`PyLongWriter_Discard` to destroy the writer instance.  Digits must
-   be in the range [``0``; ``(1 << sys.int_info.bits_per_digit) - 1``].  Unused
-   digits must be set to ``0``.
+   be in the range [``0``; ``(1 << bits_per_digit) - 1``]  (where the
+   :c:struct:`~PyLongLayout.bits_per_digit` is the number of bits per digit).
+   The unused most-significant digits must be set to ``0``.
 
 
 .. c:function:: PyObject* PyLongWriter_Finish(PyLongWriter *writer)
@@ -797,7 +798,11 @@ The :c:type:`PyLongWriter` API can be used to import an integer.
    The function takes care of normalizing the digits and converts the object
    to a compact integer if needed.
 
+   The writer instance is invalid after the call.
+
 
 .. c:function:: void PyLongWriter_Discard(PyLongWriter *writer)
 
    Discard a :c:type:`PyLongWriter` created by :c:func:`PyLongWriter_Create`.
+
+   The writer instance is invalid after the call.
diff --git a/Include/cpython/longintrepr.h b/Include/cpython/longintrepr.h
index 9c6422395664e1..357477b60d9a5a 100644
--- a/Include/cpython/longintrepr.h
+++ b/Include/cpython/longintrepr.h
@@ -145,7 +145,7 @@ typedef struct PyLongLayout {
     uint8_t bits_per_digit;
     uint8_t digit_size;
     int8_t digits_order;
-    int8_t endianness;
+    int8_t digit_endianness;
 } PyLongLayout;
 
 PyAPI_FUNC(const PyLongLayout*) PyLong_GetNativeLayout(void);
diff --git a/Lib/test/test_capi/test_long.py b/Lib/test/test_capi/test_long.py
index 894dea1d6bac25..4e6f86f3cf4b29 100644
--- a/Lib/test/test_capi/test_long.py
+++ b/Lib/test/test_capi/test_long.py
@@ -723,7 +723,7 @@ def test_long_layout(self):
             'bits_per_digit': int_info.bits_per_digit,
             'digit_size': int_info.sizeof_digit,
             'digits_order': -1,
-            'endianness': -1 if sys.byteorder == 'little' else 1,
+            'digit_endianness': -1 if sys.byteorder == 'little' else 1,
         }
         self.assertEqual(layout, expected)
 
@@ -756,7 +756,8 @@ def test_longwriter_create(self):
         base = 2 ** layout['bits_per_digit']
 
         pylongwriter_create = _testcapi.pylongwriter_create
-        self.assertEqual(pylongwriter_create(0, []), 0)
+        self.assertRaises(ValueError, pylongwriter_create, 0, [])
+        self.assertRaises(ValueError, pylongwriter_create, -123, [])
         self.assertEqual(pylongwriter_create(0, [0]), 0)
         self.assertEqual(pylongwriter_create(0, [123]), 123)
         self.assertEqual(pylongwriter_create(1, [123]), -123)
diff --git a/Modules/_testcapi/long.c b/Modules/_testcapi/long.c
index 5b20b8c08c5e2a..a5f118bd481080 100644
--- a/Modules/_testcapi/long.c
+++ b/Modules/_testcapi/long.c
@@ -180,11 +180,11 @@ layout_to_dict(const PyLongLayout *layout)
         goto error;
     }
 
-    value = PyLong_FromLong(layout->endianness);
+    value = PyLong_FromLong(layout->digit_endianness);
     if (value == NULL) {
         goto error;
     }
-    res = PyDict_SetItemString(dict, "endianness", value);
+    res = PyDict_SetItemString(dict, "digit_endianness", value);
     Py_DECREF(value);
     if (res < 0) {
         goto error;
@@ -215,7 +215,7 @@ pylong_export(PyObject *module, PyObject *obj)
     const digit *export_long_digits = export_long.digits;
 
     PyObject *digits = PyList_New(0);
-    for (Py_ssize_t i=0; i < export_long.ndigits; i++) {
+    for (Py_ssize_t i = 0; i < export_long.ndigits; i++) {
         PyObject *item = PyLong_FromUnsignedLong(export_long_digits[i]);
         if (item == NULL) {
             goto error;
@@ -258,7 +258,7 @@ pylongwriter_create(PyObject *module, PyObject *args)
         return PyErr_NoMemory();
     }
 
-    for (Py_ssize_t i=0; i < ndigits; i++) {
+    for (Py_ssize_t i = 0; i < ndigits; i++) {
         PyObject *item = PyList_GET_ITEM(list, i);
 
         long num = PyLong_AsLong(item);
diff --git a/Objects/longobject.c b/Objects/longobject.c
index 034ef08b2db9a4..c61c6ce7f57d2a 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -6781,7 +6781,7 @@ int PyLong_AsUInt64(PyObject *obj, uint64_t *value)
 static const PyLongLayout PyLong_LAYOUT = {
     .bits_per_digit = PyLong_SHIFT,
     .digits_order = -1,  // least significant first
-    .endianness = PY_LITTLE_ENDIAN ? -1 : 1,
+    .digit_endianness = PY_LITTLE_ENDIAN ? -1 : 1,
     .digit_size = sizeof(digit),
 };
 
@@ -6851,7 +6851,7 @@ PyLong_FreeExport(PyLongExport *export_long)
 PyLongWriter*
 PyLongWriter_Create(int negative, Py_ssize_t ndigits, void **digits)
 {
-    if (ndigits < 0) {
+    if (ndigits <= 0) {
         PyErr_SetString(PyExc_ValueError, "ndigits must be positive");
         return NULL;
     }
@@ -6861,9 +6861,6 @@ PyLongWriter_Create(int negative, Py_ssize_t ndigits, void **digits)
     if (obj == NULL) {
         return NULL;
     }
-    if (ndigits == 0) {
-        assert(obj->long_value.ob_digit[0] == 0);
-    }
     if (negative) {
         _PyLong_FlipSign(obj);
     }