Index: Modules/posixmodule.c
===================================================================
--- Modules/posixmodule.c	(revision 78265)
+++ Modules/posixmodule.c	(working copy)
@@ -3823,6 +3823,12 @@
 	return PyLong_FromPid(getpid());
 }
 
+#ifdef NGROUPS_MAX
+#define MAX_GROUPS NGROUPS_MAX
+#else
+      /* defined to be 16 on Solaris7, so this should be a small number */
+#define MAX_GROUPS 64
+#endif
 
 #ifdef HAVE_GETGROUPS
 PyDoc_STRVAR(posix_getgroups__doc__,
@@ -3832,18 +3838,23 @@
 static PyObject *
 posix_getgroups(PyObject *self, PyObject *noargs)
 {
-    PyObject *result = NULL;
+	PyObject *result = NULL;
+        int n;
 
-#ifdef NGROUPS_MAX
-#define MAX_GROUPS NGROUPS_MAX
+#ifdef _DARWIN_C_SOURCE
+        gid_t *grouplist = NULL;
+	n = getgroups(0, grouplist);
+	if (n > 0) {
+		grouplist = PyMem_MALLOC(n * sizeof(gid_t));
+		if (grouplist == NULL)
+			return PyErr_NoMemory();
+	}
+	n = getgroups(n, grouplist);
 #else
-        /* defined to be 16 on Solaris7, so this should be a small number */
-#define MAX_GROUPS 64
+        gid_t grouplist[MAX_GROUPS];
+        n = getgroups(MAX_GROUPS, grouplist);
 #endif
-        gid_t grouplist[MAX_GROUPS];
-        int n;
 
-        n = getgroups(MAX_GROUPS, grouplist);
         if (n < 0)
             posix_error();
         else {
@@ -3861,7 +3872,10 @@
                 }
             }
         }
-
+#ifdef _DARWIN_C_SOURCE
+	if (grouplist)
+		PyMem_FREE(grouplist);
+#endif
     return result;
 }
 #endif