diff --git a/homeassistant/helpers/config_validation.py b/homeassistant/helpers/config_validation.py
index 5b2ad0da2ac..af42b6373ba 100644
--- a/homeassistant/helpers/config_validation.py
+++ b/homeassistant/helpers/config_validation.py
@@ -286,9 +286,12 @@ def entity_domain(domain: Union[str, List[str]]) -> Callable[[Any], str]:
     """Validate that entity belong to domain."""
     ent_domain = entities_domain(domain)
 
-    def validate(value: Any) -> str:
+    def validate(value: str) -> str:
         """Test if entity domain is domain."""
-        return ent_domain(value)[0]
+        validated = ent_domain(value)
+        if len(validated) != 1:
+            raise vol.Invalid(f"Expected exactly 1 entity, got {len(validated)}")
+        return validated[0]
 
     return validate
 
diff --git a/tests/helpers/test_config_validation.py b/tests/helpers/test_config_validation.py
index c829d4413f0..7693efbb926 100644
--- a/tests/helpers/test_config_validation.py
+++ b/tests/helpers/test_config_validation.py
@@ -179,7 +179,12 @@ def test_entity_domain():
     """Test entity domain validation."""
     schema = vol.Schema(cv.entity_domain("sensor"))
 
-    for value in ("invalid_entity", "cover.demo"):
+    for value in (
+        "invalid_entity",
+        "cover.demo",
+        "cover.demo,sensor.another_entity",
+        "",
+    ):
         with pytest.raises(vol.MultipleInvalid):
             schema(value)