diff -r 0fd2ea06e17d -r dac3a1042acd Lib/test/test_format.py
--- a/Lib/test/test_format.py	Thu Dec 06 16:32:37 2012 +0200
+++ b/Lib/test/test_format.py	Thu Dec 06 10:37:54 2012 -0700
@@ -234,6 +234,16 @@
         testformat('%g', 1.1, '1.1')
         testformat('%#g', 1.1, '1.10000')
 
+        # Regression test for http://bugs.python.org/issue15516.
+        class IntFails(object):
+            def __int__(self):
+                raise TestFailed
+            def __long__(self):
+                return 0
+
+        fst = IntFails()
+        testformat("%x", fst, '0')
+
         # Test exception for unknown format characters
         if verbose:
             print 'Testing exceptions'
diff -r 0fd2ea06e17d -r dac3a1042acd Objects/stringobject.c
--- a/Objects/stringobject.c	Thu Dec 06 16:32:37 2012 +0200
+++ b/Objects/stringobject.c	Thu Dec 06 10:37:54 2012 -0700
@@ -4489,7 +4489,10 @@
                     }
                     else {
                         iobj = PyNumber_Int(v);
-                        if (iobj==NULL) iobj = PyNumber_Long(v);
+                        if (iobj==NULL) {
+			    PyErr_Clear();
+			    iobj = PyNumber_Long(v);
+			}
                     }
                     if (iobj!=NULL) {
                         if (PyInt_Check(iobj)) {