diff --git a/bobtail/response.py b/bobtail/response.py
index b51e793..48d5fd2 100644
--- a/bobtail/response.py
+++ b/bobtail/response.py
@@ -181,7 +181,7 @@ def get(self, req: Request, res: Response) -> None:
             if file_suffix in ("jpg", "jpeg", "png", "gif", "tiff", "svg+xml", "x-icon"):
                 self.set_headers({"Content-Type": f"image/{file_suffix}"})
             elif file_suffix == "css":
-                self.set_headers({"Content-Type": f"text/css"})
+                self.set_headers({"Content-Type": "text/css"})
             elif file_suffix in ("mpeg", "mp4", "quicktime", "webm", "x-ms-wmv", "x-msvideo", "x-flv"):
                 self.set_headers({"Content-Type": f"video/{file_suffix}"})
             elif file_suffix in ("mpeg", "x-ms-wma", "vnd.rn-realaudio", "x-wav"):