diff --git a/selfdrive/thermald/thermald.py b/selfdrive/thermald/thermald.py
index b80ce71aea..266b28db04 100755
--- a/selfdrive/thermald/thermald.py
+++ b/selfdrive/thermald/thermald.py
@@ -165,7 +165,7 @@ def hw_state_thread(end_event, hw_queue):
     time.sleep(DT_TRML)
 
 
-def thermald_thread(end_event, hw_queue):
+def thermald_thread(end_event, hw_queue) -> None:
   pm = messaging.PubMaster(['deviceState'])
   sm = messaging.SubMaster(["peripheralState", "gpsLocationExternal", "controlsState", "pandaStates"], poll=["pandaStates"])
 
@@ -177,10 +177,10 @@ def thermald_thread(end_event, hw_queue):
   startup_conditions: Dict[str, bool] = {}
   startup_conditions_prev: Dict[str, bool] = {}
 
-  off_ts = None
-  started_ts = None
+  off_ts: Optional[float] = None
+  started_ts: Optional[float] = None
   started_seen = False
-  startup_blocked_ts = None
+  startup_blocked_ts: Optional[float] = None
   thermal_status = ThermalStatus.yellow
 
   last_hw_state = HardwareState(