diff --git a/Include/pystate.h b/Include/pystate.h
index a8fcc73..cd1d776 100644
--- a/Include/pystate.h
+++ b/Include/pystate.h
@@ -69,6 +69,7 @@
 typedef struct _ts {
     /* See Python/ceval.c for comments explaining most fields */
 
+    struct _ts *prev;
     struct _ts *next;
     PyInterpreterState *interp;