diff -r a3f076d4f54f Modules/_elementtree.c
--- a/Modules/_elementtree.c	Fri Dec 18 10:23:29 2015 +0200
+++ b/Modules/_elementtree.c	Fri Dec 18 11:13:18 2015 +0200
@@ -3582,9 +3582,10 @@ static PyObject *
 /*[clinic end generated code: output=1440092922b13ed1 input=abf90830a1c3b0fc]*/
 {
     /* activate element event reporting */
-    Py_ssize_t i, seqlen;
+    Py_ssize_t i;
     TreeBuilderObject *target;
     PyObject *events_append, *events_seq;
+    PyObject *tmp;
 
     if (!TreeBuilder_CheckExact(self->target)) {
         PyErr_SetString(
@@ -3600,8 +3601,9 @@ static PyObject *
     events_append = PyObject_GetAttrString(events_queue, "append");
     if (events_append == NULL)
         return NULL;
-    Py_XDECREF(target->events_append);
+    tmp = target->events_append;
     target->events_append = events_append;
+    Py_XDECREF(tmp);
 
     /* clear out existing events */
     Py_CLEAR(target->start_event_obj);
@@ -3620,8 +3622,7 @@ static PyObject *
         return NULL;
     }
 
-    seqlen = PySequence_Size(events_seq);
-    for (i = 0; i < seqlen; ++i) {
+    for (i = 0; i < PySequence_Size(events_seq); ++i) {
         PyObject *event_name_obj = PySequence_Fast_GET_ITEM(events_seq, i);
         char *event_name = NULL;
         if (PyUnicode_Check(event_name_obj)) {
@@ -3629,37 +3630,41 @@ static PyObject *
         } else if (PyBytes_Check(event_name_obj)) {
             event_name = PyBytes_AS_STRING(event_name_obj);
         }
+        Py_INCREF(event_name_obj);
 
         if (event_name == NULL) {
+            Py_DECREF(event_name_obj);
             Py_DECREF(events_seq);
             PyErr_Format(PyExc_ValueError, "invalid events sequence");
             return NULL;
         } else if (strcmp(event_name, "start") == 0) {
-            Py_INCREF(event_name_obj);
+            tmp = target->start_event_obj;
             target->start_event_obj = event_name_obj;
+            Py_XDECREF(tmp);
         } else if (strcmp(event_name, "end") == 0) {
-            Py_INCREF(event_name_obj);
-            Py_XDECREF(target->end_event_obj);
+            tmp = target->end_event_obj;
             target->end_event_obj = event_name_obj;
+            Py_XDECREF(tmp);
         } else if (strcmp(event_name, "start-ns") == 0) {
-            Py_INCREF(event_name_obj);
-            Py_XDECREF(target->start_ns_event_obj);
+            tmp = target->start_ns_event_obj;
             target->start_ns_event_obj = event_name_obj;
+            Py_XDECREF(tmp);
             EXPAT(SetNamespaceDeclHandler)(
                 self->parser,
                 (XML_StartNamespaceDeclHandler) expat_start_ns_handler,
                 (XML_EndNamespaceDeclHandler) expat_end_ns_handler
                 );
         } else if (strcmp(event_name, "end-ns") == 0) {
-            Py_INCREF(event_name_obj);
-            Py_XDECREF(target->end_ns_event_obj);
+            tmp = target->end_ns_event_obj;
             target->end_ns_event_obj = event_name_obj;
+            Py_XDECREF(tmp);
             EXPAT(SetNamespaceDeclHandler)(
                 self->parser,
                 (XML_StartNamespaceDeclHandler) expat_start_ns_handler,
                 (XML_EndNamespaceDeclHandler) expat_end_ns_handler
                 );
         } else {
+            Py_DECREF(event_name_obj);
             Py_DECREF(events_seq);
             PyErr_Format(PyExc_ValueError, "unknown event '%s'", event_name);
             return NULL;