diff --git a/lightly/api/serve.py b/lightly/api/serve.py
index e0d3a3278..08960efd3 100644
--- a/lightly/api/serve.py
+++ b/lightly/api/serve.py
@@ -42,7 +42,7 @@ def do_OPTIONS(self) -> None:
             self.send_header("Access-Control-Allow-Methods", "GET, POST, OPTIONS")
             self.end_headers()
 
-        def send_response_only(self, code: int, message: str|None=None) -> None:
+        def send_response_only(self, code: int, message: str | None = None) -> None:
             super().send_response_only(code, message)
             self.send_header(
                 "Cache-Control", "no-store, must-revalidate, no-cache, max-age=-1"