diff --git a/homeassistant/components/knx/schema.py b/homeassistant/components/knx/schema.py
index c6206e883e5..a505714c0d0 100644
--- a/homeassistant/components/knx/schema.py
+++ b/homeassistant/components/knx/schema.py
@@ -101,7 +101,11 @@ def ga_validator(value: Any) -> str | int:
     )
 
 
-ga_list_validator = vol.All(cv.ensure_list, [ga_validator])
+ga_list_validator = vol.All(
+    cv.ensure_list,
+    [ga_validator],
+    vol.IsTrue("value must be a group address or a list containing group addresses"),
+)
 
 ia_validator = vol.Any(
     vol.All(str, str.strip, cv.matches_regex(IndividualAddress.ADDRESS_RE.pattern)),