diff -r 285d28c3620a Python/pystate.c
--- a/Python/pystate.c	Thu Nov 14 01:27:12 2013 +0100
+++ b/Python/pystate.c	Thu Nov 14 09:27:13 2013 +0100
@@ -771,6 +771,11 @@ PyGILState_Ensure(void)
     assert(autoInterpreterState); /* Py_Initialize() hasn't been called! */
     tcur = (PyThreadState *)PyThread_get_key_value(autoTLSkey);
     if (tcur == NULL) {
+        /* At startup, Python has no concrete GIL. If PyGILState_Ensure() is
+           called from a new thread for the first time, we need the create the
+           GIL. */
+        PyEval_InitThreads();
+
         /* Create a new thread state for this thread */
         tcur = PyThreadState_New(autoInterpreterState);
         if (tcur == NULL)