diff --git a/sygnal/gcmpushkin.py b/sygnal/gcmpushkin.py
index 01b7ae74..e3971227 100644
--- a/sygnal/gcmpushkin.py
+++ b/sygnal/gcmpushkin.py
@@ -745,7 +745,7 @@ def _build_data(
         return data
 
 
-def truncate_str(input: str, max_bytes: int) -> tuple[str, bool]:
+def truncate_str(input: str, max_bytes: int) -> Tuple[str, bool]:
     """
     Truncate the given string. If the truncation would occur in the middle of a unicode
     character, that character will be removed entirely instead.