diff --git a/Python/pystate.c b/Python/pystate.c
index d049811..98e954d 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -2,6 +2,7 @@
 /* Thread and interpreter state structures and their interfaces */
 
 #include "Python.h"
+#include "internal/mem.h"
 #include "internal/pystate.h"
 
 #define _PyThreadState_SET(value) \