diff --git a/csst_common/file.py b/csst_common/file.py
index 0197136e376fb07404776b7d9b620294cd35ef73..c1a04776b33384f5207a69bcb36fd3787f7625c3 100644
--- a/csst_common/file.py
+++ b/csst_common/file.py
@@ -99,18 +99,5 @@ class File:
     def derive2(self, *args, **kwargs):
         return self.derive(*args, **kwargs, level=2)
 
-    def replace_ext(
-        self, new_ext: Optional[str] = "img.fits", new_dir: Optional[str] = None
-    ) -> str:
-        if new_dir is None:
-            new_dir = self.new_dir
-        if new_ext is None:
-            new_ext = self.ext
-
-        if new_ext.startswith("."):
-            return os.path.join(new_dir, self.prefix + new_ext)
-        else:
-            return os.path.join(new_dir, self.prefix + "_" + new_ext)
-
     def __repr__(self):
         return f"<File {self.file_path}>"