Index: Lib/test/test_time.py
===================================================================
--- Lib/test/test_time.py	(revision 78430)
+++ Lib/test/test_time.py	(working copy)
@@ -114,6 +114,9 @@
     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_tzset(self):
         if not hasattr(time, "tzset"):
Index: Modules/timemodule.c
===================================================================
--- Modules/timemodule.c	(revision 78430)
+++ Modules/timemodule.c	(working copy)
@@ -557,18 +557,19 @@
 {
 	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))
 		return NULL;
-	p = asctime(&buf);
-	if (p[24] == '\n')
-		p[24] = '\0';
-	return PyString_FromString(p);
+	if (asctime_r(&buf, ascbuf) == NULL) {
+	        PyErr_SetString(PyExc_ValueError, "invalid time");
+		return NULL;
+	}
+	return PyString_FromStringAndSize(ascbuf, 24);
 }
 
 PyDoc_STRVAR(asctime_doc,