diff --git a/Include/pystate.h b/Include/pystate.h
index a19c1ed..29d7148 100644
--- a/Include/pystate.h
+++ b/Include/pystate.h
@@ -8,6 +8,8 @@
 extern "C" {
 #endif
 
+#include "pythread.h"
+
 /* This limitation is for performance and simplicity. If needed it can be
 removed (with effort). */
 #define MAX_CO_EXTRA_USERS 255
@@ -111,6 +113,8 @@
     struct _ts *tstate_head;
 
     int64_t id;
+    int64_t id_refcount;
+    PyThread_type_lock id_mutex;
 
     PyObject *modules;
     PyObject *modules_by_index;