diff --git a/Include/longobject.h b/Include/longobject.h
index d741f1b..9e154d1 100644
--- a/Include/longobject.h
+++ b/Include/longobject.h
@@ -49,6 +49,40 @@ PyAPI_FUNC(PyObject *) PyLong_GetInfo(void);
 #error "sizeof(pid_t) is neither sizeof(int), sizeof(long) or sizeof(long long)"
 #endif /* SIZEOF_PID_T */
 
+/* Issue #2005: uid_t can be longer than a C long on some systems */
+#if !defined(SIZEOF_UID_T) || SIZEOF_UID_T == SIZEOF_INT
+#define _Py_PARSE_UID "i"
+#define PyLong_FromUid PyLong_FromLong
+#define PyLong_AsUid PyLong_AsLong
+#elif SIZEOF_UID_T == SIZEOF_LONG
+#define _Py_PARSE_UID "l"
+#define PyLong_FromUid PyLong_FromLong
+#define PyLong_AsUid PyLong_AsLong
+#elif defined(SIZEOF_LONG_LONG) && SIZEOF_UID_T == SIZEOF_LONG_LONG
+#define _Py_PARSE_UID "L"
+#define PyLong_FromUid PyLong_FromLongLong
+#define PyLong_AsUid PyLong_AsLongLong
+#else
+#error "sizeof(uid_t) is neither sizeof(int), sizeof(long) or sizeof(long long)"
+#endif /* SIZEOF_UID_T */
+
+/* Issue #2005: gid_t can be longer than a C long on some systems */
+#if !defined(SIZEOF_GID_T) || SIZEOF_GID_T == SIZEOF_INT
+#define _Py_PARSE_GID "i"
+#define PyLong_FromGid PyLong_FromLong
+#define PyLong_AsGid PyLong_AsLong
+#elif SIZEOF_GID_T == SIZEOF_LONG
+#define _Py_PARSE_GID "l"
+#define PyLong_FromGid PyLong_FromLong
+#define PyLong_AsGid PyLong_AsLong
+#elif defined(SIZEOF_LONG_LONG) && SIZEOF_GID_T == SIZEOF_LONG_LONG
+#define _Py_PARSE_GID "L"
+#define PyLong_FromGid PyLong_FromLongLong
+#define PyLong_AsGid PyLong_AsLongLong
+#else
+#error "sizeof(gid_t) is neither sizeof(int), sizeof(long) or sizeof(long long)"
+#endif /* SIZEOF_GID_T */
+
 /* Used by Python/mystrtoul.c. */
 #ifndef Py_LIMITED_API
 PyAPI_DATA(unsigned char) _PyLong_DigitValue[256];
diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index 0fe3963..626ba7b 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -2035,8 +2035,8 @@ _pystat_fromstructstat(STRUCT_STAT *st)
     PyStructSequence_SET_ITEM(v, 2, PyLong_FromLong((long)st->st_dev));
 #endif
     PyStructSequence_SET_ITEM(v, 3, PyLong_FromLong((long)st->st_nlink));
-    PyStructSequence_SET_ITEM(v, 4, PyLong_FromLong((long)st->st_uid));
-    PyStructSequence_SET_ITEM(v, 5, PyLong_FromLong((long)st->st_gid));
+    PyStructSequence_SET_ITEM(v, 4, PyLong_FromUid((long)st->st_uid));
+    PyStructSequence_SET_ITEM(v, 5, PyLong_FromGid((long)st->st_gid));
 #ifdef HAVE_LARGEFILE_SUPPORT
     PyStructSequence_SET_ITEM(v, 6,
                               PyLong_FromLongLong((PY_LONG_LONG)st->st_size));
@@ -2839,7 +2839,6 @@ static PyObject *
 posix_chown(PyObject *self, PyObject *args, PyObject *kwargs)
 {
     path_t path;
-    long uid_l, gid_l;
     uid_t uid;
     gid_t gid;
     int dir_fd = DEFAULT_DIR_FD;
@@ -2853,9 +2852,11 @@ posix_chown(PyObject *self, PyObject *args, PyObject *kwargs)
 #ifdef HAVE_FCHOWN
     path.allow_fd = 1;
 #endif
-    if (!PyArg_ParseTupleAndKeywords(args, kwargs, "O&ll|$O&p:chown", keywords,
-                                     path_converter, &path,
-                                     &uid_l, &gid_l,
+    if (!PyArg_ParseTupleAndKeywords(args, kwargs,
+                                     "O&" _Py_PARSE_UID _Py_PARSE_GID
+                                     "|$O&p:chown",
+                                     keywords, path_converter, &path,
+                                     &uid, &gid,
 #ifdef HAVE_FCHOWNAT
                                      dir_fd_converter, &dir_fd,
 #else
@@ -2886,8 +2887,6 @@ posix_chown(PyObject *self, PyObject *args, PyObject *kwargs)
 #endif
 
     Py_BEGIN_ALLOW_THREADS
-    uid = (uid_t)uid_l;
-    gid = (uid_t)gid_l;
 #ifdef HAVE_FCHOWN
     if (path.fd != -1)
         result = fchown(path.fd, uid, gid);
@@ -2931,12 +2930,14 @@ static PyObject *
 posix_fchown(PyObject *self, PyObject *args)
 {
     int fd;
-    long uid, gid;
+    uid_t uid;
+    gid_t gid;
     int res;
-    if (!PyArg_ParseTuple(args, "ill:fchown", &fd, &uid, &gid))
+    if (!PyArg_ParseTuple(args, "i" _Py_PARSE_UID _Py_PARSE_GID ":fchown",
+                          &fd, &uid, &gid))
         return NULL;
     Py_BEGIN_ALLOW_THREADS
-    res = fchown(fd, (uid_t) uid, (gid_t) gid);
+    res = fchown(fd, uid, gid);
     Py_END_ALLOW_THREADS
     if (res < 0)
         return posix_error();
@@ -2956,15 +2957,16 @@ posix_lchown(PyObject *self, PyObject *args)
 {
     PyObject *opath;
     char *path;
-    long uid, gid;
+    uid_t uid;
+    gid_t gid;
     int res;
-    if (!PyArg_ParseTuple(args, "O&ll:lchown",
+    if (!PyArg_ParseTuple(args, "O&" _Py_PARSE_UID _Py_PARSE_GID ":lchown",
                           PyUnicode_FSConverter, &opath,
                           &uid, &gid))
         return NULL;
     path = PyBytes_AsString(opath);
     Py_BEGIN_ALLOW_THREADS
-    res = lchown(path, (uid_t) uid, (gid_t) gid);
+    res = lchown(path, uid, gid);
     Py_END_ALLOW_THREADS
     if (res < 0)
         return posix_error_with_allocated_filename(opath);
@@ -5624,7 +5626,7 @@ Return the current process's effective group id.");
 static PyObject *
 posix_getegid(PyObject *self, PyObject *noargs)
 {
-    return PyLong_FromLong((long)getegid());
+    return PyLong_FromGid(getegid());
 }
 #endif
 
@@ -5637,7 +5639,7 @@ Return the current process's effective user id.");
 static PyObject *
 posix_geteuid(PyObject *self, PyObject *noargs)
 {
-    return PyLong_FromLong((long)geteuid());
+    return PyLong_FromUid(geteuid());
 }
 #endif
 
@@ -5650,7 +5652,7 @@ Return the current process's group id.");
 static PyObject *
 posix_getgid(PyObject *self, PyObject *noargs)
 {
-    return PyLong_FromLong((long)getgid());
+    return PyLong_FromGid(getgid());
 }
 #endif
 
@@ -5820,14 +5822,14 @@ posix_initgroups(PyObject *self, PyObject *args)
     PyObject *oname;
     char *username;
     int res;
-    long gid;
+    gid_t gid;
 
-    if (!PyArg_ParseTuple(args, "O&l:initgroups",
+    if (!PyArg_ParseTuple(args, "O&" _Py_PARSE_GID ":initgroups",
                           PyUnicode_FSConverter, &oname, &gid))
         return NULL;
     username = PyBytes_AS_STRING(oname);
 
-    res = initgroups(username, (gid_t) gid);
+    res = initgroups(username, gid);
     Py_DECREF(oname);
     if (res == -1)
         return PyErr_SetFromErrno(PyExc_OSError);
@@ -6002,7 +6004,7 @@ Return the current process's user id.");
 static PyObject *
 posix_getuid(PyObject *self, PyObject *noargs)
 {
-    return PyLong_FromLong((long)getuid());
+    return PyLong_FromUid(getuid());
 }
 #endif
 
@@ -6127,15 +6129,9 @@ Set the current process's user id.");
 static PyObject *
 posix_setuid(PyObject *self, PyObject *args)
 {
-    long uid_arg;
     uid_t uid;
-    if (!PyArg_ParseTuple(args, "l:setuid", &uid_arg))
-        return NULL;
-    uid = uid_arg;
-    if (uid != uid_arg) {
-        PyErr_SetString(PyExc_OverflowError, "user id too big");
+    if (!PyArg_ParseTuple(args, _Py_PARSE_UID ":setuid", &uid))
         return NULL;
-    }
     if (setuid(uid) < 0)
         return posix_error();
     Py_INCREF(Py_None);
@@ -6152,15 +6148,9 @@ Set the current process's effective user id.");
 static PyObject *
 posix_seteuid (PyObject *self, PyObject *args)
 {
-    long euid_arg;
     uid_t euid;
-    if (!PyArg_ParseTuple(args, "l", &euid_arg))
-        return NULL;
-    euid = euid_arg;
-    if (euid != euid_arg) {
-        PyErr_SetString(PyExc_OverflowError, "user id too big");
+    if (!PyArg_ParseTuple(args, _Py_PARSE_UID, &euid))
         return NULL;
-    }
     if (seteuid(euid) < 0) {
         return posix_error();
     } else {
@@ -6178,15 +6168,9 @@ Set the current process's effective group id.");
 static PyObject *
 posix_setegid (PyObject *self, PyObject *args)
 {
-    long egid_arg;
     gid_t egid;
-    if (!PyArg_ParseTuple(args, "l", &egid_arg))
-        return NULL;
-    egid = egid_arg;
-    if (egid != egid_arg) {
-        PyErr_SetString(PyExc_OverflowError, "group id too big");
+    if (!PyArg_ParseTuple(args, _Py_PARSE_GID, &egid))
         return NULL;
-    }
     if (setegid(egid) < 0) {
         return posix_error();
     } else {
@@ -6204,23 +6188,9 @@ Set the current process's real and effective user ids.");
 static PyObject *
 posix_setreuid (PyObject *self, PyObject *args)
 {
-    long ruid_arg, euid_arg;
     uid_t ruid, euid;
-    if (!PyArg_ParseTuple(args, "ll", &ruid_arg, &euid_arg))
-        return NULL;
-    if (ruid_arg == -1)
-        ruid = (uid_t)-1;  /* let the compiler choose how -1 fits */
-    else
-        ruid = ruid_arg;  /* otherwise, assign from our long */
-    if (euid_arg == -1)
-        euid = (uid_t)-1;
-    else
-        euid = euid_arg;
-    if ((euid_arg != -1 && euid != euid_arg) ||
-        (ruid_arg != -1 && ruid != ruid_arg)) {
-        PyErr_SetString(PyExc_OverflowError, "user id too big");
+    if (!PyArg_ParseTuple(args, _Py_PARSE_UID _Py_PARSE_UID, &ruid, &euid))
         return NULL;
-    }
     if (setreuid(ruid, euid) < 0) {
         return posix_error();
     } else {
@@ -6238,23 +6208,9 @@ Set the current process's real and effective group ids.");
 static PyObject *
 posix_setregid (PyObject *self, PyObject *args)
 {
-    long rgid_arg, egid_arg;
     gid_t rgid, egid;
-    if (!PyArg_ParseTuple(args, "ll", &rgid_arg, &egid_arg))
-        return NULL;
-    if (rgid_arg == -1)
-        rgid = (gid_t)-1;  /* let the compiler choose how -1 fits */
-    else
-        rgid = rgid_arg;  /* otherwise, assign from our long */
-    if (egid_arg == -1)
-        egid = (gid_t)-1;
-    else
-        egid = egid_arg;
-    if ((egid_arg != -1 && egid != egid_arg) ||
-        (rgid_arg != -1 && rgid != rgid_arg)) {
-        PyErr_SetString(PyExc_OverflowError, "group id too big");
+    if (!PyArg_ParseTuple(args, _Py_PARSE_GID _Py_PARSE_GID, &rgid, &egid))
         return NULL;
-    }
     if (setregid(rgid, egid) < 0) {
         return posix_error();
     } else {
@@ -6272,15 +6228,9 @@ Set the current process's group id.");
 static PyObject *
 posix_setgid(PyObject *self, PyObject *args)
 {
-    long gid_arg;
     gid_t gid;
-    if (!PyArg_ParseTuple(args, "l:setgid", &gid_arg))
+    if (!PyArg_ParseTuple(args, _Py_PARSE_GID ":setgid", &gid))
         return NULL;
-    gid = gid_arg;
-    if (gid != gid_arg) {
-        PyErr_SetString(PyExc_OverflowError, "group id too big");
-        return NULL;
-    }
     if (setgid(gid) < 0)
         return posix_error();
     Py_INCREF(Py_None);
@@ -6319,21 +6269,14 @@ posix_setgroups(PyObject *self, PyObject *groups)
             Py_DECREF(elem);
             return NULL;
         } else {
-            unsigned long x = PyLong_AsUnsignedLong(elem);
+            gid_t gid = PyLong_AsGid(elem);
             if (PyErr_Occurred()) {
                 PyErr_SetString(PyExc_TypeError,
                                 "group id too big");
                 Py_DECREF(elem);
                 return NULL;
             }
-            grouplist[i] = x;
-            /* read back the value to see if it fitted in gid_t */
-            if (grouplist[i] != x) {
-                PyErr_SetString(PyExc_TypeError,
-                                "group id too big");
-                Py_DECREF(elem);
-                return NULL;
-            }
+            grouplist[i] = gid;
         }
         Py_DECREF(elem);
     }
@@ -6492,7 +6435,7 @@ posix_waitid(PyObject *self, PyObject *args)
         return NULL;
 
     PyStructSequence_SET_ITEM(result, 0, PyLong_FromPid(si.si_pid));
-    PyStructSequence_SET_ITEM(result, 1, PyLong_FromPid(si.si_uid));
+    PyStructSequence_SET_ITEM(result, 1, PyLong_FromUid(si.si_uid));
     PyStructSequence_SET_ITEM(result, 2, PyLong_FromLong((long)(si.si_signo)));
     PyStructSequence_SET_ITEM(result, 3, PyLong_FromLong((long)(si.si_status)));
     PyStructSequence_SET_ITEM(result, 4, PyLong_FromLong((long)(si.si_code)));
@@ -7007,8 +6950,9 @@ static PyObject *
 posix_setpgid(PyObject *self, PyObject *args)
 {
     pid_t pid;
-    int pgrp;
-    if (!PyArg_ParseTuple(args, _Py_PARSE_PID "i:setpgid", &pid, &pgrp))
+    pid_t pgrp;
+    if (!PyArg_ParseTuple(args, _Py_PARSE_PID _Py_PARSE_PID ":setpgid",
+                          &pid, &pgrp))
         return NULL;
     if (setpgid(pid, pgrp) < 0)
         return posix_error();
@@ -9740,9 +9684,9 @@ Set the current process's real, effective, and saved user ids.");
 static PyObject*
 posix_setresuid (PyObject *self, PyObject *args)
 {
-    /* We assume uid_t is no larger than a long. */
-    long ruid, euid, suid;
-    if (!PyArg_ParseTuple(args, "lll", &ruid, &euid, &suid))
+    uid_t ruid, euid, suid;
+    if (!PyArg_ParseTuple(args, _Py_PARSE_UID _Py_PARSE_UID _Py_PARSE_UID,
+                          &ruid, &euid, &suid))
         return NULL;
     if (setresuid(ruid, euid, suid) < 0)
         return posix_error();
@@ -9759,8 +9703,9 @@ static PyObject*
 posix_setresgid (PyObject *self, PyObject *args)
 {
     /* We assume uid_t is no larger than a long. */
-    long rgid, egid, sgid;
-    if (!PyArg_ParseTuple(args, "lll", &rgid, &egid, &sgid))
+    gid_t rgid, egid, sgid;
+    if (!PyArg_ParseTuple(args, _Py_PARSE_GID _Py_PARSE_GID _Py_PARSE_GID,
+                          &rgid, &egid, &sgid))
         return NULL;
     if (setresgid(rgid, egid, sgid) < 0)
         return posix_error();
@@ -9777,14 +9722,10 @@ static PyObject*
 posix_getresuid (PyObject *self, PyObject *noargs)
 {
     uid_t ruid, euid, suid;
-    long l_ruid, l_euid, l_suid;
     if (getresuid(&ruid, &euid, &suid) < 0)
         return posix_error();
-    /* Force the values into long's as we don't know the size of uid_t. */
-    l_ruid = ruid;
-    l_euid = euid;
-    l_suid = suid;
-    return Py_BuildValue("(lll)", l_ruid, l_euid, l_suid);
+    return Py_BuildValue("(NNN)", PyLong_FromUid(ruid), PyLong_FromUid(euid),
+                         PyLong_FromUid(suid));
 }
 #endif
 
@@ -9797,14 +9738,10 @@ static PyObject*
 posix_getresgid (PyObject *self, PyObject *noargs)
 {
     uid_t rgid, egid, sgid;
-    long l_rgid, l_egid, l_sgid;
     if (getresgid(&rgid, &egid, &sgid) < 0)
         return posix_error();
-    /* Force the values into long's as we don't know the size of uid_t. */
-    l_rgid = rgid;
-    l_egid = egid;
-    l_sgid = sgid;
-    return Py_BuildValue("(lll)", l_rgid, l_egid, l_sgid);
+    return Py_BuildValue("(NNN)", PyLong_FromGid(rgid), PyLong_FromGid(egid),
+                         PyLong_FromGid(sgid));
 }
 #endif
 
diff --git a/configure.ac b/configure.ac
index 94d5b80..5d699a0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1654,6 +1654,8 @@ AC_CHECK_SIZEOF(double, 8)
 AC_CHECK_SIZEOF(fpos_t, 4)
 AC_CHECK_SIZEOF(size_t, 4)
 AC_CHECK_SIZEOF(pid_t, 4)
+AC_CHECK_SIZEOF(uid_t, 4)
+AC_CHECK_SIZEOF(gid_t, 4)
 
 AC_MSG_CHECKING(for long long support)
 have_long_long=no