diff --git a/homeassistant/components/frontend/__init__.py b/homeassistant/components/frontend/__init__.py
index 9694c299b23..2f2a8e93b1e 100644
--- a/homeassistant/components/frontend/__init__.py
+++ b/homeassistant/components/frontend/__init__.py
@@ -26,6 +26,7 @@ from homeassistant.const import (
     EVENT_THEMES_UPDATED,
 )
 from homeassistant.core import HomeAssistant, ServiceCall, callback
+from homeassistant.exceptions import HomeAssistantError
 from homeassistant.helpers import config_validation as cv, service
 from homeassistant.helpers.icon import async_get_icons
 from homeassistant.helpers.json import json_dumps_sorted
@@ -543,6 +544,12 @@ async def _async_setup_themes(
         """Reload themes."""
         config = await async_hass_config_yaml(hass)
         new_themes = config.get(DOMAIN, {}).get(CONF_THEMES, {})
+
+        try:
+            THEME_SCHEMA(new_themes)
+        except vol.Invalid as err:
+            raise HomeAssistantError(f"Failed to reload themes: {err}") from err
+
         hass.data[DATA_THEMES] = new_themes
         if hass.data[DATA_DEFAULT_THEME] not in new_themes:
             hass.data[DATA_DEFAULT_THEME] = DEFAULT_THEME
diff --git a/tests/components/frontend/test_init.py b/tests/components/frontend/test_init.py
index f28742cdd0a..a6c35513dc3 100644
--- a/tests/components/frontend/test_init.py
+++ b/tests/components/frontend/test_init.py
@@ -26,6 +26,7 @@ from homeassistant.components.frontend import (
 )
 from homeassistant.components.websocket_api import TYPE_RESULT
 from homeassistant.core import HomeAssistant
+from homeassistant.exceptions import HomeAssistantError
 from homeassistant.loader import async_get_integration
 from homeassistant.setup import async_setup_component
 
@@ -408,6 +409,35 @@ async def test_themes_reload_themes(
     assert msg["result"]["default_theme"] == "default"
 
 
+@pytest.mark.usefixtures("frontend")
+async def test_themes_reload_invalid(
+    hass: HomeAssistant, themes_ws_client: MockHAClientWebSocket
+) -> None:
+    """Test frontend.reload_themes service with an invalid theme."""
+
+    with patch(
+        "homeassistant.components.frontend.async_hass_config_yaml",
+        return_value={DOMAIN: {CONF_THEMES: {"happy": {"primary-color": "pink"}}}},
+    ):
+        await hass.services.async_call(DOMAIN, "reload_themes", blocking=True)
+
+    with (
+        patch(
+            "homeassistant.components.frontend.async_hass_config_yaml",
+            return_value={DOMAIN: {CONF_THEMES: {"sad": "blue"}}},
+        ),
+        pytest.raises(HomeAssistantError, match="Failed to reload themes"),
+    ):
+        await hass.services.async_call(DOMAIN, "reload_themes", blocking=True)
+
+    await themes_ws_client.send_json({"id": 5, "type": "frontend/get_themes"})
+
+    msg = await themes_ws_client.receive_json()
+
+    assert msg["result"]["themes"] == {"happy": {"primary-color": "pink"}}
+    assert msg["result"]["default_theme"] == "default"
+
+
 async def test_missing_themes(ws_client: MockHAClientWebSocket) -> None:
     """Test that themes API works when themes are not defined."""
     await ws_client.send_json({"id": 5, "type": "frontend/get_themes"})