diff --git a/homeassistant/components/caldav/api.py b/homeassistant/components/caldav/api.py
index b64b7fb8e734..0f0b5a60e409 100644
--- a/homeassistant/components/caldav/api.py
+++ b/homeassistant/components/caldav/api.py
@@ -1,5 +1,4 @@
 """Library for working with CalDAV api."""
-# pylint: disable=home-assistant-use-runtime-data  # Uses legacy hass.data[DOMAIN] pattern
 
 import logging
 
@@ -8,7 +7,7 @@ from caldav.lib.error import DAVError
 
 from homeassistant.core import HomeAssistant
 
-from .const import DOMAIN
+from .const import WARNED_CALENDARS
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -45,9 +44,7 @@ async def async_get_calendars(
     calendars, needs_warning = await hass.async_add_executor_job(_get_calendars)
 
     if needs_warning:
-        warned_calendars: set[tuple[str, str]] = hass.data.setdefault(
-            DOMAIN, {}
-        ).setdefault("warned_calendars", set())
+        warned_calendars = hass.data.setdefault(WARNED_CALENDARS, set())
         for url, name, comp in needs_warning:
             # This workaround and warning can be removed when we upgrade to caldav 3.0
             if (url, comp) not in warned_calendars:
diff --git a/homeassistant/components/caldav/const.py b/homeassistant/components/caldav/const.py
index e133bb1b8bc8..5c3b512be451 100644
--- a/homeassistant/components/caldav/const.py
+++ b/homeassistant/components/caldav/const.py
@@ -2,5 +2,12 @@
 
 from typing import Final
 
+from homeassistant.util.hass_dict import HassKey
+
 DOMAIN: Final = "caldav"
 TIMEOUT: Final = 30
+
+# Calendars we have already warned about, keyed by (url, component). This is
+# deliberately not stored on a config entry: the warning is per CalDAV server
+# and must survive reloads, and the same server may back more than one entry.
+WARNED_CALENDARS: HassKey[set[tuple[str, str]]] = HassKey(f"{DOMAIN}_warned_calendars")
diff --git a/tests/components/caldav/test_init.py b/tests/components/caldav/test_init.py
index 543446b146f9..aefe6a73ecf3 100644
--- a/tests/components/caldav/test_init.py
+++ b/tests/components/caldav/test_init.py
@@ -1,12 +1,14 @@
 """Unit tests for the CalDav integration."""
 
-from unittest.mock import patch
+import logging
+from unittest.mock import MagicMock, Mock, patch
 
 from caldav.lib.error import AuthorizationError, DAVError
 import pytest
 import requests
 
 from homeassistant.config_entries import ConfigEntryState
+from homeassistant.const import Platform
 from homeassistant.core import HomeAssistant
 
 from tests.common import MockConfigEntry
@@ -71,3 +73,40 @@ async def test_client_failure(
 
     flows = hass.config_entries.flow.async_progress()
     assert [flow.get("step_id") for flow in flows] == expected_flows
+
+
+@pytest.fixture(name="calendars")
+def mock_unsupported_calendar() -> list[Mock]:
+    """Fixture for a calendar that does not report its supported components."""
+    calendar = Mock()
+    calendar.name = "Example"
+    calendar.search = MagicMock(return_value=[])
+    calendar.get_supported_components = MagicMock(side_effect=KeyError())
+    return [calendar]
+
+
+@pytest.mark.parametrize("platforms", [[Platform.CALENDAR]])
+async def test_supported_components_warning_survives_reload(
+    hass: HomeAssistant,
+    config_entry: MockConfigEntry,
+    caplog: pytest.LogCaptureFixture,
+) -> None:
+    """Test the unsupported-components warning is not repeated after a reload.
+
+    The de-duplication cache is per CalDAV server rather than per config entry,
+    so reloading the entry must not warn about the same calendar again.
+    """
+    caplog.set_level(logging.WARNING, logger="homeassistant.components.caldav.api")
+
+    await hass.config_entries.async_setup(config_entry.entry_id)
+    await hass.async_block_till_done()
+
+    assert config_entry.state is ConfigEntryState.LOADED
+    assert "does not report supported components" in caplog.text
+
+    caplog.clear()
+    await hass.config_entries.async_reload(config_entry.entry_id)
+    await hass.async_block_till_done()
+
+    assert config_entry.state is ConfigEntryState.LOADED
+    assert "does not report supported components" not in caplog.text