diff --git a/homeassistant/components/deconz/cover.py b/homeassistant/components/deconz/cover.py
index 6e5e616fbb8..7db3477c3bb 100644
--- a/homeassistant/components/deconz/cover.py
+++ b/homeassistant/components/deconz/cover.py
@@ -61,7 +61,7 @@ class DeconzCover(DeconzDevice, CoverDevice):
     @property
     def current_cover_position(self):
         """Return the current position of the cover."""
-        return 100 - int(self._device.brightness / 255 * 100)
+        return 100 - int(self._device.brightness / 254 * 100)
 
     @property
     def is_closed(self):
@@ -88,7 +88,7 @@ class DeconzCover(DeconzDevice, CoverDevice):
 
         if position < 100:
             data["on"] = True
-            data["bri"] = 255 - int(position / 100 * 255)
+            data["bri"] = 254 - int(position / 100 * 254)
 
         await self._device.async_set_state(data)
 
diff --git a/tests/components/deconz/test_cover.py b/tests/components/deconz/test_cover.py
index 4bf0ec86f4a..43bb165b1a6 100644
--- a/tests/components/deconz/test_cover.py
+++ b/tests/components/deconz/test_cover.py
@@ -14,7 +14,7 @@ COVERS = {
         "id": "Level controllable cover id",
         "name": "Level controllable cover",
         "type": "Level controllable output",
-        "state": {"bri": 255, "on": False, "reachable": True},
+        "state": {"bri": 254, "on": False, "reachable": True},
         "modelid": "Not zigbee spec",
         "uniqueid": "00:00:00:00:00:00:00:00-00",
     },
@@ -22,7 +22,7 @@ COVERS = {
         "id": "Window covering device id",
         "name": "Window covering device",
         "type": "Window covering device",
-        "state": {"bri": 255, "on": True, "reachable": True},
+        "state": {"bri": 254, "on": True, "reachable": True},
         "modelid": "lumi.curtain",
         "uniqueid": "00:00:00:00:00:00:00:01-00",
     },
@@ -33,6 +33,14 @@ COVERS = {
         "state": {"reachable": True},
         "uniqueid": "00:00:00:00:00:00:00:02-00",
     },
+    "4": {
+        "id": "deconz old brightness cover id",
+        "name": "deconz old brightness cover",
+        "type": "Level controllable output",
+        "state": {"bri": 255, "on": False, "reachable": True},
+        "modelid": "Not zigbee spec",
+        "uniqueid": "00:00:00:00:00:00:00:03-00",
+    },
 }
 
 
@@ -62,7 +70,8 @@ async def test_cover(hass):
     assert "cover.level_controllable_cover" in gateway.deconz_ids
     assert "cover.window_covering_device" in gateway.deconz_ids
     assert "cover.unsupported_cover" not in gateway.deconz_ids
-    assert len(hass.states.async_all()) == 3
+    assert "cover.deconz_old_brightness_cover" in gateway.deconz_ids
+    assert len(hass.states.async_all()) == 4
 
     level_controllable_cover = hass.states.get("cover.level_controllable_cover")
     assert level_controllable_cover.state == "open"
@@ -105,7 +114,7 @@ async def test_cover(hass):
         )
         await hass.async_block_till_done()
         set_callback.assert_called_with(
-            "put", "/lights/1/state", json={"on": True, "bri": 255}
+            "put", "/lights/1/state", json={"on": True, "bri": 254}
         )
 
     with patch.object(
@@ -120,6 +129,23 @@ async def test_cover(hass):
         await hass.async_block_till_done()
         set_callback.assert_called_with("put", "/lights/1/state", json={"bri_inc": 0})
 
+    """Test that a reported cover position of 255 (deconz-rest-api < 2.05.73) is interpreted correctly."""
+    deconz_old_brightness_cover = hass.states.get("cover.deconz_old_brightness_cover")
+    assert deconz_old_brightness_cover.state == "open"
+
+    state_changed_event = {
+        "t": "event",
+        "e": "changed",
+        "r": "lights",
+        "id": "4",
+        "state": {"on": True},
+    }
+    gateway.api.event_handler(state_changed_event)
+    await hass.async_block_till_done()
+
+    deconz_old_brightness_cover = hass.states.get("cover.deconz_old_brightness_cover")
+    assert deconz_old_brightness_cover.attributes["current_position"] == 0
+
     await gateway.async_reset()
 
     assert len(hass.states.async_all()) == 0