diff --git a/lib/charms/operator_libs_linux/v0/apt.py b/lib/charms/operator_libs_linux/v0/apt.py
index 92fa63d..a6cf907 100644
--- a/lib/charms/operator_libs_linux/v0/apt.py
+++ b/lib/charms/operator_libs_linux/v0/apt.py
@@ -983,7 +983,7 @@ def filename(self, fname: str) -> None:
         Args:
             fname: a filename to write the repository information to.
         """
-        if not fname.endswith(".list") or fname.endswith(".sources"):
+        if not fname.endswith((".list", ".sources")):
             raise InvalidSourceError("apt source filenames should end in .list or .sources!")
         self._filename = fname