diff --git a/Include/cpython/fileutils.h b/Include/cpython/fileutils.h
index 7ab2290184a..b386ad107bd 100644
--- a/Include/cpython/fileutils.h
+++ b/Include/cpython/fileutils.h
@@ -2,165 +2,7 @@
 #  error "this header file must not be included directly"
 #endif
 
-typedef enum {
-    _Py_ERROR_UNKNOWN=0,
-    _Py_ERROR_STRICT,
-    _Py_ERROR_SURROGATEESCAPE,
-    _Py_ERROR_REPLACE,
-    _Py_ERROR_IGNORE,
-    _Py_ERROR_BACKSLASHREPLACE,
-    _Py_ERROR_SURROGATEPASS,
-    _Py_ERROR_XMLCHARREFREPLACE,
-    _Py_ERROR_OTHER
-} _Py_error_handler;
-
-PyAPI_FUNC(_Py_error_handler) _Py_GetErrorHandler(const char *errors);
-
-PyAPI_FUNC(int) _Py_DecodeLocaleEx(
-    const char *arg,
-    wchar_t **wstr,
-    size_t *wlen,
-    const char **reason,
-    int current_locale,
-    _Py_error_handler errors);
-
-PyAPI_FUNC(int) _Py_EncodeLocaleEx(
-    const wchar_t *text,
-    char **str,
-    size_t *error_pos,
-    const char **reason,
-    int current_locale,
-    _Py_error_handler errors);
-
-PyAPI_FUNC(char*) _Py_EncodeLocaleRaw(
-    const wchar_t *text,
-    size_t *error_pos);
-
-PyAPI_FUNC(PyObject *) _Py_device_encoding(int);
-
-#if defined(MS_WINDOWS) || defined(__APPLE__)
-    /* On Windows, the count parameter of read() is an int (bpo-9015, bpo-9611).
-       On macOS 10.13, read() and write() with more than INT_MAX bytes
-       fail with EINVAL (bpo-24658). */
-#   define _PY_READ_MAX  INT_MAX
-#   define _PY_WRITE_MAX INT_MAX
-#else
-    /* write() should truncate the input to PY_SSIZE_T_MAX bytes,
-       but it's safer to do it ourself to have a portable behaviour */
-#   define _PY_READ_MAX  PY_SSIZE_T_MAX
-#   define _PY_WRITE_MAX PY_SSIZE_T_MAX
-#endif
-
-#ifdef MS_WINDOWS
-struct _Py_stat_struct {
-    unsigned long st_dev;
-    uint64_t st_ino;
-    unsigned short st_mode;
-    int st_nlink;
-    int st_uid;
-    int st_gid;
-    unsigned long st_rdev;
-    __int64 st_size;
-    time_t st_atime;
-    int st_atime_nsec;
-    time_t st_mtime;
-    int st_mtime_nsec;
-    time_t st_ctime;
-    int st_ctime_nsec;
-    unsigned long st_file_attributes;
-    unsigned long st_reparse_tag;
-};
-#else
-#  define _Py_stat_struct stat
-#endif
-
-PyAPI_FUNC(int) _Py_fstat(
-    int fd,
-    struct _Py_stat_struct *status);
-
-PyAPI_FUNC(int) _Py_fstat_noraise(
-    int fd,
-    struct _Py_stat_struct *status);
-
-PyAPI_FUNC(int) _Py_stat(
-    PyObject *path,
-    struct stat *status);
-
-PyAPI_FUNC(int) _Py_open(
-    const char *pathname,
-    int flags);
-
-PyAPI_FUNC(int) _Py_open_noraise(
-    const char *pathname,
-    int flags);
-
-PyAPI_FUNC(FILE *) _Py_wfopen(
-    const wchar_t *path,
-    const wchar_t *mode);
-
+// Used by _testcapi which must not use the internal C API
 PyAPI_FUNC(FILE*) _Py_fopen_obj(
     PyObject *path,
     const char *mode);
-
-PyAPI_FUNC(Py_ssize_t) _Py_read(
-    int fd,
-    void *buf,
-    size_t count);
-
-PyAPI_FUNC(Py_ssize_t) _Py_write(
-    int fd,
-    const void *buf,
-    size_t count);
-
-PyAPI_FUNC(Py_ssize_t) _Py_write_noraise(
-    int fd,
-    const void *buf,
-    size_t count);
-
-#ifdef HAVE_READLINK
-PyAPI_FUNC(int) _Py_wreadlink(
-    const wchar_t *path,
-    wchar_t *buf,
-    /* Number of characters of 'buf' buffer
-       including the trailing NUL character */
-    size_t buflen);
-#endif
-
-#ifdef HAVE_REALPATH
-PyAPI_FUNC(wchar_t*) _Py_wrealpath(
-    const wchar_t *path,
-    wchar_t *resolved_path,
-    /* Number of characters of 'resolved_path' buffer
-       including the trailing NUL character */
-    size_t resolved_path_len);
-#endif
-
-PyAPI_FUNC(wchar_t*) _Py_wgetcwd(
-    wchar_t *buf,
-    /* Number of characters of 'buf' buffer
-       including the trailing NUL character */
-    size_t buflen);
-
-PyAPI_FUNC(int) _Py_get_inheritable(int fd);
-
-PyAPI_FUNC(int) _Py_set_inheritable(int fd, int inheritable,
-                                    int *atomic_flag_works);
-
-PyAPI_FUNC(int) _Py_set_inheritable_async_safe(int fd, int inheritable,
-                                               int *atomic_flag_works);
-
-PyAPI_FUNC(int) _Py_dup(int fd);
-
-#ifndef MS_WINDOWS
-PyAPI_FUNC(int) _Py_get_blocking(int fd);
-
-PyAPI_FUNC(int) _Py_set_blocking(int fd, int blocking);
-#else   /* MS_WINDOWS */
-PyAPI_FUNC(void*) _Py_get_osfhandle_noraise(int fd);
-
-PyAPI_FUNC(void*) _Py_get_osfhandle(int fd);
-
-PyAPI_FUNC(int) _Py_open_osfhandle_noraise(void *handle, int flags);
-
-PyAPI_FUNC(int) _Py_open_osfhandle(void *handle, int flags);
-#endif  /* MS_WINDOWS */
diff --git a/Include/internal/pycore_fileutils.h b/Include/internal/pycore_fileutils.h
index 38df73b745b..61c11a8b2d3 100644
--- a/Include/internal/pycore_fileutils.h
+++ b/Include/internal/pycore_fileutils.h
@@ -10,6 +10,165 @@ extern "C" {
 
 #include <locale.h>   /* struct lconv */
 
+typedef enum {
+    _Py_ERROR_UNKNOWN=0,
+    _Py_ERROR_STRICT,
+    _Py_ERROR_SURROGATEESCAPE,
+    _Py_ERROR_REPLACE,
+    _Py_ERROR_IGNORE,
+    _Py_ERROR_BACKSLASHREPLACE,
+    _Py_ERROR_SURROGATEPASS,
+    _Py_ERROR_XMLCHARREFREPLACE,
+    _Py_ERROR_OTHER
+} _Py_error_handler;
+
+PyAPI_FUNC(_Py_error_handler) _Py_GetErrorHandler(const char *errors);
+
+PyAPI_FUNC(int) _Py_DecodeLocaleEx(
+    const char *arg,
+    wchar_t **wstr,
+    size_t *wlen,
+    const char **reason,
+    int current_locale,
+    _Py_error_handler errors);
+
+PyAPI_FUNC(int) _Py_EncodeLocaleEx(
+    const wchar_t *text,
+    char **str,
+    size_t *error_pos,
+    const char **reason,
+    int current_locale,
+    _Py_error_handler errors);
+
+PyAPI_FUNC(char*) _Py_EncodeLocaleRaw(
+    const wchar_t *text,
+    size_t *error_pos);
+
+PyAPI_FUNC(PyObject *) _Py_device_encoding(int);
+
+#if defined(MS_WINDOWS) || defined(__APPLE__)
+    /* On Windows, the count parameter of read() is an int (bpo-9015, bpo-9611).
+       On macOS 10.13, read() and write() with more than INT_MAX bytes
+       fail with EINVAL (bpo-24658). */
+#   define _PY_READ_MAX  INT_MAX
+#   define _PY_WRITE_MAX INT_MAX
+#else
+    /* write() should truncate the input to PY_SSIZE_T_MAX bytes,
+       but it's safer to do it ourself to have a portable behaviour */
+#   define _PY_READ_MAX  PY_SSIZE_T_MAX
+#   define _PY_WRITE_MAX PY_SSIZE_T_MAX
+#endif
+
+#ifdef MS_WINDOWS
+struct _Py_stat_struct {
+    unsigned long st_dev;
+    uint64_t st_ino;
+    unsigned short st_mode;
+    int st_nlink;
+    int st_uid;
+    int st_gid;
+    unsigned long st_rdev;
+    __int64 st_size;
+    time_t st_atime;
+    int st_atime_nsec;
+    time_t st_mtime;
+    int st_mtime_nsec;
+    time_t st_ctime;
+    int st_ctime_nsec;
+    unsigned long st_file_attributes;
+    unsigned long st_reparse_tag;
+};
+#else
+#  define _Py_stat_struct stat
+#endif
+
+PyAPI_FUNC(int) _Py_fstat(
+    int fd,
+    struct _Py_stat_struct *status);
+
+PyAPI_FUNC(int) _Py_fstat_noraise(
+    int fd,
+    struct _Py_stat_struct *status);
+
+PyAPI_FUNC(int) _Py_stat(
+    PyObject *path,
+    struct stat *status);
+
+PyAPI_FUNC(int) _Py_open(
+    const char *pathname,
+    int flags);
+
+PyAPI_FUNC(int) _Py_open_noraise(
+    const char *pathname,
+    int flags);
+
+PyAPI_FUNC(FILE *) _Py_wfopen(
+    const wchar_t *path,
+    const wchar_t *mode);
+
+PyAPI_FUNC(Py_ssize_t) _Py_read(
+    int fd,
+    void *buf,
+    size_t count);
+
+PyAPI_FUNC(Py_ssize_t) _Py_write(
+    int fd,
+    const void *buf,
+    size_t count);
+
+PyAPI_FUNC(Py_ssize_t) _Py_write_noraise(
+    int fd,
+    const void *buf,
+    size_t count);
+
+#ifdef HAVE_READLINK
+PyAPI_FUNC(int) _Py_wreadlink(
+    const wchar_t *path,
+    wchar_t *buf,
+    /* Number of characters of 'buf' buffer
+       including the trailing NUL character */
+    size_t buflen);
+#endif
+
+#ifdef HAVE_REALPATH
+PyAPI_FUNC(wchar_t*) _Py_wrealpath(
+    const wchar_t *path,
+    wchar_t *resolved_path,
+    /* Number of characters of 'resolved_path' buffer
+       including the trailing NUL character */
+    size_t resolved_path_len);
+#endif
+
+PyAPI_FUNC(wchar_t*) _Py_wgetcwd(
+    wchar_t *buf,
+    /* Number of characters of 'buf' buffer
+       including the trailing NUL character */
+    size_t buflen);
+
+PyAPI_FUNC(int) _Py_get_inheritable(int fd);
+
+PyAPI_FUNC(int) _Py_set_inheritable(int fd, int inheritable,
+                                    int *atomic_flag_works);
+
+PyAPI_FUNC(int) _Py_set_inheritable_async_safe(int fd, int inheritable,
+                                               int *atomic_flag_works);
+
+PyAPI_FUNC(int) _Py_dup(int fd);
+
+#ifndef MS_WINDOWS
+PyAPI_FUNC(int) _Py_get_blocking(int fd);
+
+PyAPI_FUNC(int) _Py_set_blocking(int fd, int blocking);
+#else   /* MS_WINDOWS */
+PyAPI_FUNC(void*) _Py_get_osfhandle_noraise(int fd);
+
+PyAPI_FUNC(void*) _Py_get_osfhandle(int fd);
+
+PyAPI_FUNC(int) _Py_open_osfhandle_noraise(void *handle, int flags);
+
+PyAPI_FUNC(int) _Py_open_osfhandle(void *handle, int flags);
+#endif  /* MS_WINDOWS */
+
 // This is used after getting NULL back from Py_DecodeLocale().
 #define DECODE_LOCALE_ERR(NAME, LEN) \
     ((LEN) == (size_t)-2) \
diff --git a/Include/internal/pycore_unicodeobject.h b/Include/internal/pycore_unicodeobject.h
index 97d11aeb820..3b6dfe9dbba 100644
--- a/Include/internal/pycore_unicodeobject.h
+++ b/Include/internal/pycore_unicodeobject.h
@@ -8,6 +8,8 @@ extern "C" {
 #  error "this header requires Py_BUILD_CORE define"
 #endif
 
+#include "pycore_fileutils.h"     // _Py_error_handler
+
 
 /* runtime lifecycle */
 
diff --git a/Lib/test/test_codecs.py b/Lib/test/test_codecs.py
index f924826db94..4ad24dbb9a9 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -15,6 +15,10 @@
     import _testcapi
 except ImportError:
     _testcapi = None
+try:
+    import _testinternalcapi
+except ImportError:
+    _testinternalcapi = None
 
 try:
     import ctypes
@@ -3345,7 +3349,7 @@ def test_seeking_write(self):
         self.assertEqual(sr.readline(), b'789\n')
 
 
-@unittest.skipIf(_testcapi is None, 'need _testcapi module')
+@unittest.skipIf(_testinternalcapi is None, 'need _testinternalcapi module')
 class LocaleCodecTest(unittest.TestCase):
     """
     Test indirectly _Py_DecodeUTF8Ex() and _Py_EncodeUTF8Ex().
@@ -3359,7 +3363,7 @@ class LocaleCodecTest(unittest.TestCase):
     SURROGATES = "\uDC80\uDCFF"
 
     def encode(self, text, errors="strict"):
-        return _testcapi.EncodeLocaleEx(text, 0, errors)
+        return _testinternalcapi.EncodeLocaleEx(text, 0, errors)
 
     def check_encode_strings(self, errors):
         for text in self.STRINGS:
@@ -3399,7 +3403,7 @@ def test_encode_unsupported_error_handler(self):
         self.assertEqual(str(cm.exception), 'unsupported error handler')
 
     def decode(self, encoded, errors="strict"):
-        return _testcapi.DecodeLocaleEx(encoded, 0, errors)
+        return _testinternalcapi.DecodeLocaleEx(encoded, 0, errors)
 
     def check_decode_strings(self, errors):
         is_utf8 = (self.ENCODING == "utf-8")
diff --git a/Modules/_testcapimodule.c b/Modules/_testcapimodule.c
index be40d68b40b..ea9c048554d 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -5417,98 +5417,6 @@ bad_get(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 }
 
 
-static PyObject *
-encode_locale_ex(PyObject *self, PyObject *args)
-{
-    PyObject *unicode;
-    int current_locale = 0;
-    wchar_t *wstr;
-    PyObject *res = NULL;
-    const char *errors = NULL;
-
-    if (!PyArg_ParseTuple(args, "U|is", &unicode, &current_locale, &errors)) {
-        return NULL;
-    }
-    wstr = PyUnicode_AsWideCharString(unicode, NULL);
-    if (wstr == NULL) {
-        return NULL;
-    }
-    _Py_error_handler error_handler = _Py_GetErrorHandler(errors);
-
-    char *str = NULL;
-    size_t error_pos;
-    const char *reason = NULL;
-    int ret = _Py_EncodeLocaleEx(wstr,
-                                 &str, &error_pos, &reason,
-                                 current_locale, error_handler);
-    PyMem_Free(wstr);
-
-    switch(ret) {
-    case 0:
-        res = PyBytes_FromString(str);
-        PyMem_RawFree(str);
-        break;
-    case -1:
-        PyErr_NoMemory();
-        break;
-    case -2:
-        PyErr_Format(PyExc_RuntimeError, "encode error: pos=%zu, reason=%s",
-                     error_pos, reason);
-        break;
-    case -3:
-        PyErr_SetString(PyExc_ValueError, "unsupported error handler");
-        break;
-    default:
-        PyErr_SetString(PyExc_ValueError, "unknown error code");
-        break;
-    }
-    return res;
-}
-
-
-static PyObject *
-decode_locale_ex(PyObject *self, PyObject *args)
-{
-    char *str;
-    int current_locale = 0;
-    PyObject *res = NULL;
-    const char *errors = NULL;
-
-    if (!PyArg_ParseTuple(args, "y|is", &str, &current_locale, &errors)) {
-        return NULL;
-    }
-    _Py_error_handler error_handler = _Py_GetErrorHandler(errors);
-
-    wchar_t *wstr = NULL;
-    size_t wlen = 0;
-    const char *reason = NULL;
-    int ret = _Py_DecodeLocaleEx(str,
-                                 &wstr, &wlen, &reason,
-                                 current_locale, error_handler);
-
-    switch(ret) {
-    case 0:
-        res = PyUnicode_FromWideChar(wstr, wlen);
-        PyMem_RawFree(wstr);
-        break;
-    case -1:
-        PyErr_NoMemory();
-        break;
-    case -2:
-        PyErr_Format(PyExc_RuntimeError, "decode error: pos=%zu, reason=%s",
-                     wlen, reason);
-        break;
-    case -3:
-        PyErr_SetString(PyExc_ValueError, "unsupported error handler");
-        break;
-    default:
-        PyErr_SetString(PyExc_ValueError, "unknown error code");
-        break;
-    }
-    return res;
-}
-
-
 #ifdef Py_REF_DEBUG
 static PyObject *
 negative_refcount(PyObject *self, PyObject *Py_UNUSED(args))
@@ -6125,8 +6033,6 @@ static PyMethodDef TestMethods[] = {
     {"test_pythread_tss_key_state", test_pythread_tss_key_state, METH_VARARGS},
     {"hamt", new_hamt, METH_NOARGS},
     {"bad_get", (PyCFunction)(void(*)(void))bad_get, METH_FASTCALL},
-    {"EncodeLocaleEx", encode_locale_ex, METH_VARARGS},
-    {"DecodeLocaleEx", decode_locale_ex, METH_VARARGS},
 #ifdef Py_REF_DEBUG
     {"negative_refcount", negative_refcount, METH_NOARGS},
 #endif
diff --git a/Modules/_testinternalcapi.c b/Modules/_testinternalcapi.c
index 19babb06f56..9deba3558bf 100644
--- a/Modules/_testinternalcapi.c
+++ b/Modules/_testinternalcapi.c
@@ -399,6 +399,98 @@ get_getpath_codeobject(PyObject *self, PyObject *Py_UNUSED(args)) {
 }
 
 
+static PyObject *
+encode_locale_ex(PyObject *self, PyObject *args)
+{
+    PyObject *unicode;
+    int current_locale = 0;
+    wchar_t *wstr;
+    PyObject *res = NULL;
+    const char *errors = NULL;
+
+    if (!PyArg_ParseTuple(args, "U|is", &unicode, &current_locale, &errors)) {
+        return NULL;
+    }
+    wstr = PyUnicode_AsWideCharString(unicode, NULL);
+    if (wstr == NULL) {
+        return NULL;
+    }
+    _Py_error_handler error_handler = _Py_GetErrorHandler(errors);
+
+    char *str = NULL;
+    size_t error_pos;
+    const char *reason = NULL;
+    int ret = _Py_EncodeLocaleEx(wstr,
+                                 &str, &error_pos, &reason,
+                                 current_locale, error_handler);
+    PyMem_Free(wstr);
+
+    switch(ret) {
+    case 0:
+        res = PyBytes_FromString(str);
+        PyMem_RawFree(str);
+        break;
+    case -1:
+        PyErr_NoMemory();
+        break;
+    case -2:
+        PyErr_Format(PyExc_RuntimeError, "encode error: pos=%zu, reason=%s",
+                     error_pos, reason);
+        break;
+    case -3:
+        PyErr_SetString(PyExc_ValueError, "unsupported error handler");
+        break;
+    default:
+        PyErr_SetString(PyExc_ValueError, "unknown error code");
+        break;
+    }
+    return res;
+}
+
+
+static PyObject *
+decode_locale_ex(PyObject *self, PyObject *args)
+{
+    char *str;
+    int current_locale = 0;
+    PyObject *res = NULL;
+    const char *errors = NULL;
+
+    if (!PyArg_ParseTuple(args, "y|is", &str, &current_locale, &errors)) {
+        return NULL;
+    }
+    _Py_error_handler error_handler = _Py_GetErrorHandler(errors);
+
+    wchar_t *wstr = NULL;
+    size_t wlen = 0;
+    const char *reason = NULL;
+    int ret = _Py_DecodeLocaleEx(str,
+                                 &wstr, &wlen, &reason,
+                                 current_locale, error_handler);
+
+    switch(ret) {
+    case 0:
+        res = PyUnicode_FromWideChar(wstr, wlen);
+        PyMem_RawFree(wstr);
+        break;
+    case -1:
+        PyErr_NoMemory();
+        break;
+    case -2:
+        PyErr_Format(PyExc_RuntimeError, "decode error: pos=%zu, reason=%s",
+                     wlen, reason);
+        break;
+    case -3:
+        PyErr_SetString(PyExc_ValueError, "unsupported error handler");
+        break;
+    default:
+        PyErr_SetString(PyExc_ValueError, "unknown error code");
+        break;
+    }
+    return res;
+}
+
+
 static PyMethodDef TestMethods[] = {
     {"get_configs", get_configs, METH_NOARGS},
     {"get_recursion_depth", get_recursion_depth, METH_NOARGS},
@@ -413,6 +505,8 @@ static PyMethodDef TestMethods[] = {
     {"test_edit_cost", test_edit_cost, METH_NOARGS},
     {"normalize_path", normalize_path, METH_O, NULL},
     {"get_getpath_codeobject", get_getpath_codeobject, METH_NOARGS, NULL},
+    {"EncodeLocaleEx", encode_locale_ex, METH_VARARGS},
+    {"DecodeLocaleEx", decode_locale_ex, METH_VARARGS},
     {NULL, NULL} /* sentinel */
 };
 
diff --git a/Modules/_tracemalloc.c b/Modules/_tracemalloc.c
index 68e5f0d52dd..b838439a9cb 100644
--- a/Modules/_tracemalloc.c
+++ b/Modules/_tracemalloc.c
@@ -1,8 +1,9 @@
 #include "Python.h"
+#include "pycore_fileutils.h"     // _Py_write_noraise()
 #include "pycore_gc.h"            // PyGC_Head
+#include "pycore_hashtable.h"     // _Py_hashtable_t
 #include "pycore_pymem.h"         // _Py_tracemalloc_config
 #include "pycore_traceback.h"
-#include "pycore_hashtable.h"
 #include <pycore_frame.h>
 
 #include <stdlib.h>               // malloc()
diff --git a/Modules/mmapmodule.c b/Modules/mmapmodule.c
index 742bcb3d145..7c9c28f7fab 100644
--- a/Modules/mmapmodule.c
+++ b/Modules/mmapmodule.c
@@ -18,8 +18,13 @@
  / ftp://squirl.nightmare.com/pub/python/python-ext.
 */
 
+#ifndef Py_BUILD_CORE_BUILTIN
+#  define Py_BUILD_CORE_MODULE 1
+#endif
+
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
+#include "pycore_fileutils.h"     // _Py_stat_struct
 #include "structmember.h"         // PyMemberDef
 #include <stddef.h>               // offsetof()
 
diff --git a/Modules/ossaudiodev.c b/Modules/ossaudiodev.c
index 4bab9a58eb1..c9e788fd704 100644
--- a/Modules/ossaudiodev.c
+++ b/Modules/ossaudiodev.c
@@ -17,8 +17,13 @@
  * $Id$
  */
 
+#ifndef Py_BUILD_CORE_BUILTIN
+#  define Py_BUILD_CORE_MODULE 1
+#endif
+
 #define PY_SSIZE_T_CLEAN
 #include "Python.h"
+#include "pycore_fileutils.h"     // _Py_write()
 #include "structmember.h"         // PyMemberDef
 
 #include <stdlib.h>               // getenv()
diff --git a/Modules/selectmodule.c b/Modules/selectmodule.c
index ff1c028d0d6..367e299f83a 100644
--- a/Modules/selectmodule.c
+++ b/Modules/selectmodule.c
@@ -4,11 +4,16 @@
    have any value except INVALID_SOCKET.
 */
 
+#ifndef Py_BUILD_CORE_BUILTIN
+#  define Py_BUILD_CORE_MODULE 1
+#endif
+
 #if defined(HAVE_POLL_H) && !defined(_GNU_SOURCE)
-#define _GNU_SOURCE
+#  define _GNU_SOURCE
 #endif
 
 #include "Python.h"
+#include "pycore_fileutils.h"     // _Py_set_inheritable()
 #include "structmember.h"         // PyMemberDef
 
 #ifdef HAVE_SYS_DEVPOLL_H
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 89e93c58187..ed83f5c8262 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -85,6 +85,10 @@ Local naming conventions:
 
 */
 
+#ifndef Py_BUILD_CORE_BUILTIN
+#  define Py_BUILD_CORE_MODULE 1
+#endif
+
 #ifdef __APPLE__
 // Issue #35569: Expose RFC 3542 socket options.
 #define __APPLE_USE_RFC_3542 1
@@ -103,6 +107,7 @@ Local naming conventions:
 
 #define PY_SSIZE_T_CLEAN
 #include "Python.h"
+#include "pycore_fileutils.h"     // _Py_set_inheritable()
 #include "structmember.h"         // PyMemberDef
 
 #ifdef _Py_MEMORY_SANITIZER
diff --git a/Programs/_freeze_module.c b/Programs/_freeze_module.c
index d50787666f8..b2f1a24016f 100644
--- a/Programs/_freeze_module.c
+++ b/Programs/_freeze_module.c
@@ -11,6 +11,7 @@
 
 #include <Python.h>
 #include <marshal.h>
+#include "pycore_fileutils.h"     // _Py_stat_struct
 #include <pycore_import.h>
 
 #include <stdio.h>
diff --git a/Python/bootstrap_hash.c b/Python/bootstrap_hash.c
index 144f7cb4a21..3a2a7318086 100644
--- a/Python/bootstrap_hash.c
+++ b/Python/bootstrap_hash.c
@@ -1,5 +1,7 @@
 #include "Python.h"
 #include "pycore_initconfig.h"
+#include "pycore_fileutils.h"     // _Py_fstat_noraise()
+
 #ifdef MS_WINDOWS
 #  include <windows.h>
 #  include <bcrypt.h>