diff --git a/homeassistant/components/api/__init__.py b/homeassistant/components/api/__init__.py
index 10cf63b701d..6aead6e109f 100644
--- a/homeassistant/components/api/__init__.py
+++ b/homeassistant/components/api/__init__.py
@@ -30,7 +30,13 @@ from homeassistant.const import (
 )
 import homeassistant.core as ha
 from homeassistant.core import HomeAssistant
-from homeassistant.exceptions import ServiceNotFound, TemplateError, Unauthorized
+from homeassistant.exceptions import (
+    InvalidEntityFormatError,
+    InvalidStateError,
+    ServiceNotFound,
+    TemplateError,
+    Unauthorized,
+)
 from homeassistant.helpers import config_validation as cv, template
 from homeassistant.helpers.json import json_dumps
 from homeassistant.helpers.service import async_get_all_descriptions
@@ -236,7 +242,7 @@ class APIEntityStateView(HomeAssistantView):
         """Update state of entity."""
         if not request["hass_user"].is_admin:
             raise Unauthorized(entity_id=entity_id)
-        hass = request.app["hass"]
+        hass: HomeAssistant = request.app["hass"]
         try:
             data = await request.json()
         except ValueError:
@@ -251,9 +257,16 @@ class APIEntityStateView(HomeAssistantView):
         is_new_state = hass.states.get(entity_id) is None
 
         # Write state
-        hass.states.async_set(
-            entity_id, new_state, attributes, force_update, self.context(request)
-        )
+        try:
+            hass.states.async_set(
+                entity_id, new_state, attributes, force_update, self.context(request)
+            )
+        except InvalidEntityFormatError:
+            return self.json_message(
+                "Invalid entity ID specified.", HTTPStatus.BAD_REQUEST
+            )
+        except InvalidStateError:
+            return self.json_message("Invalid state specified.", HTTPStatus.BAD_REQUEST)
 
         # Read the state back for our response
         status_code = HTTPStatus.CREATED if is_new_state else HTTPStatus.OK
diff --git a/tests/components/api/test_init.py b/tests/components/api/test_init.py
index 38528b335b0..2d570540341 100644
--- a/tests/components/api/test_init.py
+++ b/tests/components/api/test_init.py
@@ -97,6 +97,28 @@ async def test_api_state_change_of_non_existing_entity(
     assert hass.states.get("test_entity.that_does_not_exist").state == new_state
 
 
+async def test_api_state_change_with_bad_entity_id(
+    hass: HomeAssistant, mock_api_client: TestClient
+) -> None:
+    """Test if API sends appropriate error if we omit state."""
+    resp = await mock_api_client.post(
+        "/api/states/bad.entity.id", json={"state": "new_state"}
+    )
+
+    assert resp.status == HTTPStatus.BAD_REQUEST
+
+
+async def test_api_state_change_with_bad_state(
+    hass: HomeAssistant, mock_api_client: TestClient
+) -> None:
+    """Test if API sends appropriate error if we omit state."""
+    resp = await mock_api_client.post(
+        "/api/states/test.test", json={"state": "x" * 256}
+    )
+
+    assert resp.status == HTTPStatus.BAD_REQUEST
+
+
 async def test_api_state_change_with_bad_data(
     hass: HomeAssistant, mock_api_client: TestClient
 ) -> None: