Comment 1 for bug 472338

The fix for this is to modify line 435 of block_template.c change it from:

Py_BLOCK_THREADS;
PyObject *ctr = PyObject_CallObject(self->counter, NULL);
if (ctr == NULL) {
 free(buffer);
 return NULL;
}

to

PyObject *ctr;
Py_BLOCK_THREADS;
ctr = PyObject_CallObject(self->counter, NULL);
if (ctr == NULL) {
 free(buffer);
 return NULL;
}

Build and install, then run a test. Everything should work.