diff --git a/homeassistant/components/smarttub/binary_sensor.py b/homeassistant/components/smarttub/binary_sensor.py
index 7ab343d2015..76cbd21f946 100644
--- a/homeassistant/components/smarttub/binary_sensor.py
+++ b/homeassistant/components/smarttub/binary_sensor.py
@@ -1,4 +1,6 @@
 """Platform for binary sensor integration."""
+from __future__ import annotations
+
 import logging
 
 from smarttub import SpaError, SpaReminder
@@ -144,7 +146,7 @@ class SmartTubError(SmartTubEntity, BinarySensorEntity):
         )
 
     @property
-    def error(self) -> SpaError:
+    def error(self) -> SpaError | None:
         """Return the underlying SpaError object for this entity."""
         errors = self.coordinator.data[self.spa.id][ATTR_ERRORS]
         if len(errors) == 0: