Closes #15512: Correct __sizeof__ support for parser
diff --git a/Include/node.h b/Include/node.h
index e23e709..9f6760c 100644
--- a/Include/node.h
+++ b/Include/node.h
@@ -20,6 +20,9 @@
 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);
+#endif
 
 /* Node access functions */
 #define NCH(n)		((n)->n_nchildren)