diff --git a/Include/node.h b/Include/node.h
index 99c13f7dc90..2e4e2bada7f 100644
--- a/Include/node.h
+++ b/Include/node.h
@@ -21,7 +21,7 @@ PyAPI_FUNC(int) PyNode_AddChild(node *n, int type,
                                       char *str, int lineno, int col_offset);
 PyAPI_FUNC(void) PyNode_Free(node *n);
 #ifndef Py_LIMITED_API
-Py_ssize_t _PyNode_SizeOf(node *n);
+PyAPI_FUNC(Py_ssize_t) _PyNode_SizeOf(node *n);
 #endif
 
 /* Node access functions */