diff --git a/homeassistant/components/unifi/services.py b/homeassistant/components/unifi/services.py
index c1a6bdd3a53..ecf7c33c7ba 100644
--- a/homeassistant/components/unifi/services.py
+++ b/homeassistant/components/unifi/services.py
@@ -93,7 +93,11 @@ async def async_remove_clients(hass, data) -> None:
 
         for client in controller.api.clients_all.values():
 
-            if client.last_seen - client.first_seen > 900:
+            if (
+                client.last_seen
+                and client.first_seen
+                and client.last_seen - client.first_seen > 900
+            ):
                 continue
 
             if any({client.fixed_ip, client.hostname, client.name}):
diff --git a/tests/components/unifi/test_services.py b/tests/components/unifi/test_services.py
index 8fe41d7a856..b483e789f96 100644
--- a/tests/components/unifi/test_services.py
+++ b/tests/components/unifi/test_services.py
@@ -197,6 +197,9 @@ async def test_reconnect_wired_client(hass, aioclient_mock):
 async def test_remove_clients(hass, aioclient_mock):
     """Verify removing different variations of clients work."""
     clients = [
+        {
+            "mac": "00:00:00:00:00:00",
+        },
         {
             "first_seen": 100,
             "last_seen": 500,
@@ -239,7 +242,7 @@ async def test_remove_clients(hass, aioclient_mock):
     await hass.services.async_call(UNIFI_DOMAIN, SERVICE_REMOVE_CLIENTS, blocking=True)
     assert aioclient_mock.mock_calls[0][2] == {
         "cmd": "forget-sta",
-        "macs": ["00:00:00:00:00:01"],
+        "macs": ["00:00:00:00:00:00", "00:00:00:00:00:01"],
     }
 
     assert await hass.config_entries.async_unload(config_entry.entry_id)