diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6eabbb0ce8..df8779e30c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,7 +9,7 @@ v2025.12.0で行われた「configの`trustProxy`のデフォルト値を`false`
 - 依存関係の更新
 
 ### Client
--
+- Fix: バージョン表記のないPlayが正しく動作しない問題を修正
 
 ### Server
 -
diff --git a/packages/frontend/src/pages/flash/flash.vue b/packages/frontend/src/pages/flash/flash.vue
index 2913aaae64..efc9ee014f 100644
--- a/packages/frontend/src/pages/flash/flash.vue
+++ b/packages/frontend/src/pages/flash/flash.vue
@@ -193,7 +193,7 @@ function start() {
 }
 
 function getIsLegacy(version: string | null): boolean {
-	if (version == null) return false;
+	if (version == null) return true;
 	try {
 		return compareVersions(version, '1.0.0') < 0;
 	} catch {
@@ -206,7 +206,7 @@ async function run() {
 	if (!flash.value) return;
 
 	const version = utils.getLangVersion(flash.value.script);
-	const isLegacy = version != null && getIsLegacy(version);
+	const isLegacy = getIsLegacy(version);
 
 	const { Interpreter, Parser, values } = isLegacy ? (await import('@syuilo/aiscript-0-19-0') as any) : await import('@syuilo/aiscript');