diff --git a/Lib/test/test_format.py b/Lib/test/test_format.py
index 2959447..a9b3170 100644
--- a/Lib/test/test_format.py
+++ b/Lib/test/test_format.py
@@ -230,6 +230,14 @@
 test_exc(u'no format', u'1', TypeError,
          "not all arguments converted during string formatting")
 
+class Foobar(long):
+    def __oct__(self):
+        # Returning a non-string should not blow up.
+        return self + 1
+
+test_exc('%o', Foobar(), TypeError,
+         "expected string or Unicode object, long found")
+
 if sys.maxint == 2**31-1:
     # crashes 2.2.1 and earlier:
     try:
diff --git a/Misc/NEWS b/Misc/NEWS
index f81389d..5894c16 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,8 @@
 Core and builtins
 -----------------
 
+- Fix segfault when doing string formatting on subclasses of long.
+
 - Fix bug related to __len__ functions using values > 2**32 on 64-bit machines
   with new-style classes.
   
diff --git a/Objects/stringobject.c b/Objects/stringobject.c
index bbbeaa6..2189a82 100644
--- a/Objects/stringobject.c
+++ b/Objects/stringobject.c
@@ -4225,12 +4225,15 @@
 	if (!result)
 		return NULL;
 
+	buf = PyString_AsString(result);
+	if (!buf)
+		return NULL;
+
 	/* To modify the string in-place, there can only be one reference. */
 	if (result->ob_refcnt != 1) {
 		PyErr_BadInternalCall();
 		return NULL;
 	}
-	buf = PyString_AsString(result);
 	llen = PyString_Size(result);
 	if (llen > PY_SSIZE_T_MAX) {
 		PyErr_SetString(PyExc_ValueError, "string too large in _PyString_FormatLong");