Index: Lib/test/test_time.py
===================================================================
--- Lib/test/test_time.py	(revision 87690)
+++ Lib/test/test_time.py	(working copy)
@@ -123,33 +123,22 @@
         time.asctime(time.gmtime(self.t))
         self.assertRaises(TypeError, time.asctime, 0)
         self.assertRaises(TypeError, time.asctime, ())
-        # XXX: POSIX-compliant asctime should refuse to convert year > 9999,
-        # but glibc implementation does not.  For now, just check it doesn't
-        # segfault as it did before, and the result contains no newline.
-        try:
-            result = time.asctime((12345, 1, 0, 0, 0, 0, 0, 0, 0))
-        except ValueError:
-            # for POSIX-compliant runtimes
-            pass
-        else:
-            self.assertNotIn('\n', result)
+        self.assertRaises(ValueError, time.asctime, (12345,) + (0,) * 8)
 
     def test_asctime_bounding_check(self):
         self._bounds_checking(time.asctime)
 
     def test_ctime(self):
-        # XXX: POSIX-compliant ctime should refuse to convert year > 9999,
-        # but glibc implementation does not.  For now, just check it doesn't
-        # segfault as it did before, and the result contains no newline.
-        try:
-            result = time.ctime(1e12)
-        except ValueError:
-            # for POSIX-compliant runtimes (or 32-bit systems, where time_t
-            # cannot hold timestamps with a five-digit year)
-            pass
-        else:
-            self.assertNotIn('\n', result)
+        self.assertRaises(ValueError, time.ctime, 1e12)
 
+        # The following constant is time.mktime((10000, 1, 10, ..)).
+        # We don't compute it here because mktime may fail on some
+        # platforms for large years.  Hopefully no sane TZ will bring
+        # this date to a valid range.
+        bigval = 253403078400
+        self.assertRaises(ValueError, time.ctime, bigval)
+
+
     @unittest.skipIf(not hasattr(time, "tzset"),
         "time module has no attribute tzset")
     def test_tzset(self):
Index: Modules/timemodule.c
===================================================================
--- Modules/timemodule.c	(revision 87690)
+++ Modules/timemodule.c	(working copy)
@@ -611,7 +611,7 @@
 {
     PyObject *tup = NULL;
     struct tm buf;
-    char *p, *q;
+    char *p;
     if (!PyArg_UnpackTuple(args, "asctime", 0, 1, &tup))
         return NULL;
     if (tup == NULL) {
@@ -619,17 +619,15 @@
         buf = *localtime(&tt);
     } else if (!gettmarg(tup, &buf) || !checktm(&buf))
         return NULL;
-    p = asctime(&buf);
-    if (p == NULL) {
-        PyErr_SetString(PyExc_ValueError, "unconvertible time");
+    if (buf.tm_year + 1900 > 9999 ||
+        buf.tm_year + 1900 < -999) {
+        PyErr_SetString(PyExc_ValueError, "year out of range");
         return NULL;
     }
-    /* Replace a terminating newline by a null byte, normally at position 24.
-     * It can occur later if the year has more than four digits. */
-    for (q = p+24; *q != '\0'; q++)
-        if (*q == '\n')
-            *q = '\0';
-    return PyUnicode_FromString(p);
+    p = asctime(&buf);
+    assert(p != NULL);
+    assert(p[24] == '\n');
+    return PyUnicode_FromStringAndSize(p, 24);
 }
 
 PyDoc_STRVAR(asctime_doc,
@@ -644,7 +642,8 @@
 {
     PyObject *ot = NULL;
     time_t tt;
-    char *p, *q;
+    char *p;
+    struct tm *pbuf;
 
     if (!PyArg_UnpackTuple(args, "ctime", 0, 1, &ot))
         return NULL;
@@ -658,17 +657,26 @@
         if (tt == (time_t)-1 && PyErr_Occurred())
             return NULL;
     }
-    p = ctime(&tt);
-    if (p == NULL) {
+    pbuf = localtime(&tt);
+    if (pbuf == NULL) {
         PyErr_SetString(PyExc_ValueError, "unconvertible time");
+        return NULL;        
+    }
+    /* XXX: localtime should not return a struct tm that is not valid input
+     * for asctime on a given platform, but out of abundance of caution, we
+     * check the fields here.
+     */
+    if (!checktm(pbuf))
         return NULL;
+    if (pbuf->tm_year + 1900 > 9999 ||
+        pbuf->tm_year + 1900 < -999) {
+        PyErr_SetString(PyExc_ValueError, "year out of range");
+        return NULL;
     }
-    /* Replace a terminating newline by a null byte, normally at position 24.
-     * It can occur later if the year has more than four digits. */
-    for (q = p+24; *q != '\0'; q++)
-        if (*q == '\n')
-            *q = '\0';
-    return PyUnicode_FromString(p);
+    p = asctime(pbuf);
+    assert(p != NULL);
+    assert(p[24] == '\n');
+    return PyUnicode_FromStringAndSize(p, 24);
 }
 
 PyDoc_STRVAR(ctime_doc,