diff -r bc1a178b3bc8 Objects/genobject.c
--- a/Objects/genobject.c	Sat Apr 18 05:54:02 2015 +0200
+++ b/Objects/genobject.c	Sat Apr 18 21:43:06 2015 +0200
@@ -396,13 +396,21 @@
 
     if (PyErr_ExceptionMatches(PyExc_StopIteration)) {
         PyErr_Fetch(&et, &ev, &tb);
-        Py_XDECREF(et);
-        Py_XDECREF(tb);
         if (ev) {
+            if (!PyObject_IsInstance(ev, PyExc_StopIteration)) {
+                /* normalisation wasn't done yet -> do it now! */
+                PyErr_NormalizeException(&et, &ev, &tb);
+                if (!PyObject_IsInstance(ev, PyExc_StopIteration)) {
+                    PyErr_Restore(et, ev, tb);
+                    return -1;
+                }
+            }
             value = ((PyStopIterationObject *)ev)->value;
             Py_INCREF(value);
             Py_DECREF(ev);
         }
+        Py_XDECREF(et);
+        Py_XDECREF(tb);
     } else if (PyErr_Occurred()) {
         return -1;
     }