diff --git a/plugwise/constants.py b/plugwise/constants.py
index 90f20b11d2..752d2600d9 100644
--- a/plugwise/constants.py
+++ b/plugwise/constants.py
@@ -333,6 +333,13 @@
     "heater_electric",
 )
 
+SpecialType = Literal[
+    "c_heating_state",
+    "thermostat_supports_cooling",
+]
+
+SPECIALS: Final[tuple[str, ...]] = get_args(SpecialType)
+
 SPECIAL_FORMAT: Final[tuple[str, ...]] = (ENERGY_KILO_WATT_HOUR, VOLUME_CUBIC_METERS)
 
 SwitchType = Literal[
@@ -511,6 +518,7 @@ class DeviceData(TypedDict, total=False):
     domestic_hot_water_setpoint: float
     elga_status_code: int
     c_heating_state: bool
+    thermostat_supports_cooling: bool
 
     # Device availability
     available: bool | None
diff --git a/plugwise/helper.py b/plugwise/helper.py
index 28c0cd3584..4b1e06eb07 100644
--- a/plugwise/helper.py
+++ b/plugwise/helper.py
@@ -46,6 +46,7 @@
     POWER_WATT,
     SENSORS,
     SPECIAL_PLUG_TYPES,
+    SPECIALS,
     SWITCH_GROUP_TYPES,
     SWITCHES,
     TEMP_CELSIUS,
@@ -61,6 +62,7 @@
     GatewayData,
     ModelData,
     SensorType,
+    SpecialType,
     SwitchType,
     ThermoLoc,
     ToggleNameType,
@@ -860,11 +862,10 @@ def _appliance_measurements(
                         sw_key = cast(SwitchType, measurement)
                         sw_value = appl_p_loc.text in ["on", "true"]
                         data["switches"][sw_key] = sw_value
-                    case _ as measurement if measurement in (
-                        "c_heating_state", "thermostat_supports_cooling"
-                    ):
-                        value = appl_p_loc.text in ["on", "true"]
-                        data[measurement] = value
+                    case _ as measurement if measurement in SPECIALS:
+                        sp_key = cast(SpecialType, measurement)
+                        sp_value = appl_p_loc.text in ["on", "true"]
+                        data[sp_key] = sp_value
                     case "elga_status_code":
                         data["elga_status_code"] = int(appl_p_loc.text)