diff --git a/voicevox_engine/app/middlewares.py b/voicevox_engine/app/middlewares.py
index 14fd9e1f2..a26423464 100644
--- a/voicevox_engine/app/middlewares.py
+++ b/voicevox_engine/app/middlewares.py
@@ -29,7 +29,7 @@ async def global_execution_handler(request: Request, exc: Exception) -> Response
 
     # CORS用のヘッダを生成するミドルウェア
     localhost_regex = (
-        r"^[a-zA-Z+\-\.]+://(([^/]+\.)localhost|127\.0\.0\.1|\[::1\])(:[0-9]+)?$"
+        r"^[a-zA-Z+\-\.]+://(([^/]+\.)?localhost|127\.0\.0\.1|\[::1\])(:[0-9]+)?$"
     )
     compiled_localhost_regex = re.compile(localhost_regex)
     allowed_origins = ["*"]