diff -r 0f827775f7b7 Modules/posixmodule.c
--- a/Modules/posixmodule.c	Wed Feb 13 21:17:13 2013 -0500
+++ b/Modules/posixmodule.c	Thu Feb 14 11:01:49 2013 +0200
@@ -391,7 +391,17 @@
 {
     if (uid == (uid_t)-1)
         return PyLong_FromLong(-1);
+#if !defined(SIZEOF_UID_T) || SIZEOF_UID_T <= SIZEOF_LONG
+    if ((uid_t)-1 <= (uid_t)0)
+        return PyLong_FromLong(uid);
     return PyLong_FromUnsignedLong(uid);
+#elif defined(SIZEOF_LONG_LONG) && SIZEOF_UID_T <= SIZEOF_LONG_LONG
+    if ((uid_t)-1 <= (uid_t)0)
+        return PyLong_FromLongLong(uid);
+    return PyLong_FromUnsignedLong(uid);
+#else
+#  error "sizeof(uid_t) is too large"
+#endif
 }
 
 PyObject *
@@ -399,20 +409,53 @@
 {
     if (gid == (gid_t)-1)
         return PyLong_FromLong(-1);
+#if !defined(SIZEOF_GID_T) || SIZEOF_GID_T <= SIZEOF_LONG
+    if ((gid_t)-1 <= (gid_t)0)
+        return PyLong_FromLong(gid);
     return PyLong_FromUnsignedLong(gid);
+#elif defined(SIZEOF_LONG_LONG) && SIZEOF_GID_T <= SIZEOF_LONG_LONG
+    if ((gid_t)-1 <= (gid_t)0)
+        return PyLong_FromLongLong(gid);
+    return PyLong_FromUnsignedLong(gid);
+#else
+#  error "sizeof(gid_t) is too large"
+#endif
 }
 
 int
 _Py_Uid_Converter(PyObject *obj, void *p)
 {
+#ifndef SIZEOF_UID_T
+#  define USE_LONG_LONG 0
+#  define CHECK_INT_OVERFLOW (SIZEOF_INT < SIZEOF_LONG)
+#elif SIZEOF_UID_T == SIZEOF_LONG
+#  define USE_LONG_LONG 0
+#  define CHECK_INT_OVERFLOW 0
+#elif SIZEOF_UID_T == SIZEOF_INT
+#  define USE_LONG_LONG 0
+#  define CHECK_INT_OVERFLOW 1
+#elif defined(SIZEOF_LONG_LONG) && SIZEOF_UID_T == SIZEOF_LONG_LONG
+#  define USE_LONG_LONG 1
+#  define CHECK_INT_OVERFLOW 0
+#else
+#  error "sizeof(uid_t) is neither sizeof(int), sizeof(long) or sizeof(long long)"
+#endif
     int overflow;
+#if USE_LONG_LONG
+    PY_LONG_LONG result;
+#else
     long result;
+#endif
     if (PyFloat_Check(obj)) {
         PyErr_SetString(PyExc_TypeError,
                         "integer argument expected, got float");
         return 0;
     }
+#if USE_LONG_LONG
+    result = PyLong_AsLongLongAndOverflow(obj, &overflow);
+#else
     result = PyLong_AsLongAndOverflow(obj, &overflow);
+#endif
     if (overflow < 0)
         goto OverflowDown;
     if (!overflow && result == -1) {
@@ -421,11 +464,31 @@
             return 0;
         *(uid_t *)p = (uid_t)-1;
     }
+    else if ((uid_t)-1 <= (uid_t)0) {
+        /* signed uid_t */
+        if (overflow > 0)
+            goto OverflowUp;
+#if CHECK_INT_OVERFLOW
+        if (result < INT_MIN)
+            goto OverflowDown;
+        if (result > INT_MAX)
+            goto OverflowUp;
+#endif
+        *(uid_t *)p = (uid_t)result;
+    }
     else {
         /* unsigned uid_t */
+#if USE_LONG_LONG
+        unsigned PY_LONG_LONG uresult;
+#else
         unsigned long uresult;
+#endif
         if (overflow > 0) {
+#if USE_LONG_LONG
+            uresult = PyLong_AsUnsignedLongLong(obj);
+#else
             uresult = PyLong_AsUnsignedLong(obj);
+#endif
             if (PyErr_Occurred()) {
                 if (PyErr_ExceptionMatches(PyExc_OverflowError))
                     goto OverflowUp;
@@ -437,10 +500,11 @@
             if (result < 0)
                 goto OverflowDown;
             uresult = result;
-        }
-        if (sizeof(uid_t) < sizeof(long) &&
-            (unsigned long)(uid_t)uresult != uresult)
-            goto OverflowUp;
+#if CHECK_INT_OVERFLOW
+            if (uresult > UINT_MAX)
+                goto OverflowUp;
+#endif
+        }
         *(uid_t *)p = (uid_t)uresult;
     }
     return 1;
@@ -454,19 +518,44 @@
     PyErr_SetString(PyExc_OverflowError,
                     "user id is greater than maximum");
     return 0;
+#undef USE_LONG_LONG
+#undef CHECK_INT_OVERFLOW
 }
 
 int
 _Py_Gid_Converter(PyObject *obj, void *p)
 {
+#ifndef SIZEOF_GID_T
+#  define USE_LONG_LONG 0
+#  define CHECK_INT_OVERFLOW (SIZEOF_INT < SIZEOF_LONG)
+#elif SIZEOF_GID_T == SIZEOF_LONG
+#  define USE_LONG_LONG 0
+#  define CHECK_INT_OVERFLOW 0
+#elif SIZEOF_GID_T == SIZEOF_INT
+#  define USE_LONG_LONG 0
+#  define CHECK_INT_OVERFLOW 1
+#elif defined(SIZEOF_LONG_LONG) && SIZEOF_GID_T == SIZEOF_LONG_LONG
+#  define USE_LONG_LONG 1
+#  define CHECK_INT_OVERFLOW 0
+#else
+#  error "sizeof(gid_t) is neither sizeof(int), sizeof(long) or sizeof(long long)"
+#endif
     int overflow;
+#if USE_LONG_LONG
+    PY_LONG_LONG result;
+#else
     long result;
+#endif
     if (PyFloat_Check(obj)) {
         PyErr_SetString(PyExc_TypeError,
                         "integer argument expected, got float");
         return 0;
     }
+#if USE_LONG_LONG
+    result = PyLong_AsLongLongAndOverflow(obj, &overflow);
+#else
     result = PyLong_AsLongAndOverflow(obj, &overflow);
+#endif
     if (overflow < 0)
         goto OverflowDown;
     if (!overflow && result == -1) {
@@ -475,11 +564,31 @@
             return 0;
         *(gid_t *)p = (gid_t)-1;
     }
+    else if ((gid_t)-1 <= (gid_t)0) {
+        /* signed gid_t */
+        if (overflow > 0)
+            goto OverflowUp;
+#if CHECK_INT_OVERFLOW
+        if (result < INT_MIN)
+            goto OverflowDown;
+        if (result > INT_MAX)
+            goto OverflowUp;
+#endif
+        *(gid_t *)p = (gid_t)result;
+    }
     else {
         /* unsigned gid_t */
+#if USE_LONG_LONG
+        unsigned PY_LONG_LONG uresult;
+#else
         unsigned long uresult;
+#endif
         if (overflow > 0) {
+#if USE_LONG_LONG
+            uresult = PyLong_AsUnsignedLongLong(obj);
+#else
             uresult = PyLong_AsUnsignedLong(obj);
+#endif
             if (PyErr_Occurred()) {
                 if (PyErr_ExceptionMatches(PyExc_OverflowError))
                     goto OverflowUp;
@@ -491,10 +600,11 @@
             if (result < 0)
                 goto OverflowDown;
             uresult = result;
-        }
-        if (sizeof(gid_t) < sizeof(long) &&
-            (unsigned long)(gid_t)uresult != uresult)
-            goto OverflowUp;
+#if CHECK_INT_OVERFLOW
+            if (uresult > UINT_MAX)
+                goto OverflowUp;
+#endif
+        }
         *(gid_t *)p = (gid_t)uresult;
     }
     return 1;
@@ -508,6 +618,8 @@
     PyErr_SetString(PyExc_OverflowError,
                     "group id is greater than maximum");
     return 0;
+#undef USE_LONG_LONG
+#undef CHECK_INT_OVERFLOW
 }
 #endif /* MS_WINDOWS */
 
diff -r 0f827775f7b7 configure.ac
--- a/configure.ac	Wed Feb 13 21:17:13 2013 -0500
+++ b/configure.ac	Thu Feb 14 11:01:49 2013 +0200
@@ -1687,6 +1687,8 @@
 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
diff -r 0f827775f7b7 pyconfig.h.in
--- a/pyconfig.h.in	Wed Feb 13 21:17:13 2013 -0500
+++ b/pyconfig.h.in	Thu Feb 14 11:01:49 2013 +0200
@@ -1223,6 +1223,12 @@
 /* The size of `pid_t', as computed by sizeof. */
 #undef SIZEOF_PID_T
 
+/* The size of `uid_t', as computed by sizeof. */
+#undef SIZEOF_UID_T
+
+/* The size of `gid_t', as computed by sizeof. */
+#undef SIZEOF_GID_T
+
 /* The size of `pthread_t', as computed by sizeof. */
 #undef SIZEOF_PTHREAD_T