diff --git a/jambo/schema_converter.py b/jambo/schema_converter.py
index c2c8cae..3a93bc6 100644
--- a/jambo/schema_converter.py
+++ b/jambo/schema_converter.py
@@ -138,9 +138,8 @@ class SchemaConverter:
         
         type_value = schema.get("type")
         if isinstance(type_value, list):
-            raise InternalAssertionException(
-                "SchemaConverter._get_schema_type: 'type' field should not be a list here."
-                " This should have been normalized earlier."
+            raise InvalidSchemaException(
+                "Invalid schema: 'type' cannot be a list at the top level", invalid_field=str(schema)
             )
 
         return type_value
diff --git a/tests/test_schema_converter.py b/tests/test_schema_converter.py
index 01c18be..3bfe327 100644
--- a/tests/test_schema_converter.py
+++ b/tests/test_schema_converter.py
@@ -1045,5 +1045,14 @@ class TestSchemaConverter(TestCase):
             },
         }
 
+        with self.assertRaises(InvalidSchemaException):
+            self.converter.build_with_cache(schema)
+
+    def test_parse_list_type_root_level_throws(self):
+        schema = {
+            "title": "TestListType",
+            "type": ["string", "number"]
+        }
+
         with self.assertRaises(InvalidSchemaException):
             self.converter.build_with_cache(schema)
\ No newline at end of file