Index: Lib/test/test_time.py
===================================================================
--- Lib/test/test_time.py	(Revision 87613)
+++ Lib/test/test_time.py	(Arbeitskopie)
@@ -122,6 +122,9 @@
     def test_asctime(self):
         time.asctime(time.gmtime(self.t))
         self.assertRaises(TypeError, time.asctime, 0)
+        self.assertRaises(TypeError, time.asctime, ())
+        self.assertRaises(ValueError, time.asctime,
+                          (12345, 1, 0, 0, 0, 0, 0, 0, 0))
 
     def test_asctime_bounding_check(self):
         self._bounds_checking(time.asctime)
Index: Modules/timemodule.c
===================================================================
--- Modules/timemodule.c	(Revision 87613)
+++ Modules/timemodule.c	(Arbeitskopie)
@@ -611,18 +611,19 @@
 {
     PyObject *tup = NULL;
     struct tm buf;
-    char *p;
+    char ascbuf[26]; /* e.g. "Sun Sep 16 01:03:52 1973\n\0" */
     if (!PyArg_UnpackTuple(args, "asctime", 0, 1, &tup))
         return NULL;
     if (tup == NULL) {
         time_t tt = time(NULL);
-        buf = *localtime(&tt);
+        (void)localtime_r(&tt, &buf);
     } else if (!gettmarg(tup, &buf) || !checktm(&buf))
         return NULL;
-    p = asctime(&buf);
-    if (p[24] == '\n')
-        p[24] = '\0';
-    return PyUnicode_FromString(p);
+    if (asctime_r(&buf, ascbuf) == NULL) {
+        PyErr_SetString(PyExc_ValueError, "invalid time");
+        return NULL;
+    }
+    return PyUnicode_FromStringAndSize(ascbuf, 24);
 }
 
 PyDoc_STRVAR(asctime_doc,