diff -r dc0811953034 Modules/_io/bytesio.c
--- a/Modules/_io/bytesio.c	Fri Mar 25 12:50:54 2016 +0100
+++ b/Modules/_io/bytesio.c	Fri Mar 25 14:31:42 2016 +0100
@@ -909,6 +909,9 @@ bytesio_setstate(bytesio *self, PyObject
 static void
 bytesio_dealloc(bytesio *self)
 {
+    if (_PyIOBase_finalize((PyObject *) self) < 0)
+        return;
+
     _PyObject_GC_UNTRACK(self);
     if (self->exports > 0) {
         PyErr_SetString(PyExc_SystemError,
@@ -1062,8 +1065,8 @@ PyTypeObject PyBytesIO_Type = {
     0,                                         /*tp_getattro*/
     0,                                         /*tp_setattro*/
     0,                                         /*tp_as_buffer*/
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE |
-    Py_TPFLAGS_HAVE_GC,                        /*tp_flags*/
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC
+        | Py_TPFLAGS_HAVE_FINALIZE,            /*tp_flags*/
     _io_BytesIO___init____doc__,               /*tp_doc*/
     (traverseproc)bytesio_traverse,            /*tp_traverse*/
     (inquiry)bytesio_clear,                    /*tp_clear*/
diff -r dc0811953034 Modules/_io/stringio.c
--- a/Modules/_io/stringio.c	Fri Mar 25 12:50:54 2016 +0100
+++ b/Modules/_io/stringio.c	Fri Mar 25 14:31:42 2016 +0100
@@ -639,6 +639,9 @@ stringio_clear(stringio *self)
 static void
 stringio_dealloc(stringio *self)
 {
+    if (_PyIOBase_finalize((PyObject *) self) < 0)
+        return;
+
     _PyObject_GC_UNTRACK(self);
     self->ok = 0;
     if (self->buf) {
@@ -1062,8 +1065,8 @@ PyTypeObject PyStringIO_Type = {
     0,                                         /*tp_getattro*/
     0,                                         /*tp_setattro*/
     0,                                         /*tp_as_buffer*/
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
-                       | Py_TPFLAGS_HAVE_GC,   /*tp_flags*/
+    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC
+        | Py_TPFLAGS_HAVE_FINALIZE,            /*tp_flags*/
     _io_StringIO___init____doc__,              /*tp_doc*/
     (traverseproc)stringio_traverse,           /*tp_traverse*/
     (inquiry)stringio_clear,                   /*tp_clear*/