diff --git a/thermostat.py b/thermostat.py
index 58f5518..f4b1387 100644
--- a/thermostat.py
+++ b/thermostat.py
@@ -161,7 +161,7 @@ def get_forced_mode(cursor):
   if row is None:
     return None
   data = dict(zip(['value', 'timestamp'], row))
-  timestamp = data['timestamp'].replace(tzinfo=timezone.utc).timestamp()
+  timestamp = datetime.fromisoformat(data['timestamp']).replace(tzinfo=timezone.utc).timestamp()
   # We ignore old targets but never ignore absence modes
   if data['value'] in targets and time.time() - timestamp > forced_mode_duration:
     logging.debug("Ignoring old set mode.")