diff --git a/Zend/zend_ast.h b/Zend/zend_ast.h
index 0bbb3a820c291..4c1a87e288a73 100644
--- a/Zend/zend_ast.h
+++ b/Zend/zend_ast.h
@@ -313,7 +313,7 @@ typedef void (*zend_ast_apply_func)(zend_ast **ast_ptr, void *context);
 ZEND_API void zend_ast_apply(zend_ast *ast, zend_ast_apply_func fn, void *context);
 
 static zend_always_inline size_t zend_ast_size(uint32_t children) {
-	return sizeof(zend_ast) - sizeof(zend_ast *) + sizeof(zend_ast *) * children;
+	return XtOffsetOf(zend_ast, child) + (sizeof(zend_ast *) * children);
 }
 
 static zend_always_inline bool zend_ast_is_special(zend_ast *ast) {
diff --git a/ext/opcache/zend_persist.c b/ext/opcache/zend_persist.c
index c8330c1e79057..b10e5a8046ab1 100644
--- a/ext/opcache/zend_persist.c
+++ b/ext/opcache/zend_persist.c
@@ -188,7 +188,7 @@ static zend_ast *zend_persist_ast(zend_ast *ast)
 		node = (zend_ast *) copy;
 	} else {
 		uint32_t children = zend_ast_get_num_children(ast);
-		node = zend_shared_memdup(ast, sizeof(zend_ast) - sizeof(zend_ast *) + sizeof(zend_ast *) * children);
+		node = zend_shared_memdup(ast, zend_ast_size(children));
 		for (i = 0; i < children; i++) {
 			if (node->child[i]) {
 				node->child[i] = zend_persist_ast(node->child[i]);
diff --git a/ext/opcache/zend_persist_calc.c b/ext/opcache/zend_persist_calc.c
index dfc281eb7f6f7..2d4a3c92afa29 100644
--- a/ext/opcache/zend_persist_calc.c
+++ b/ext/opcache/zend_persist_calc.c
@@ -87,7 +87,7 @@ static void zend_persist_ast_calc(zend_ast *ast)
 		}
 	} else {
 		uint32_t children = zend_ast_get_num_children(ast);
-		ADD_SIZE(sizeof(zend_ast) - sizeof(zend_ast *) + sizeof(zend_ast *) * children);
+		ADD_SIZE(zend_ast_size(children));
 		for (i = 0; i < children; i++) {
 			if (ast->child[i]) {
 				zend_persist_ast_calc(ast->child[i]);