diff --git a/homeassistant/components/evohome/__init__.py b/homeassistant/components/evohome/__init__.py
index e436268db63..9af53981957 100644
--- a/homeassistant/components/evohome/__init__.py
+++ b/homeassistant/components/evohome/__init__.py
@@ -107,7 +107,7 @@ def _dt_aware_to_naive(dt_aware: dt) -> dt:
     return dt_naive.replace(microsecond=0)
 
 
-def convert_until(status_dict: dict, until_key: str) -> str:
+def convert_until(status_dict: dict, until_key: str) -> None:
     """Reformat a dt str from "%Y-%m-%dT%H:%M:%SZ" as local/aware/isoformat."""
     if until_key in status_dict:  # only present for certain modes
         dt_utc_naive = dt_util.parse_datetime(status_dict[until_key])