diff --git a/jambo/schema_converter.py b/jambo/schema_converter.py
index 39a5848..1f9834f 100644
--- a/jambo/schema_converter.py
+++ b/jambo/schema_converter.py
@@ -77,7 +77,7 @@ class SchemaConverter:
         return fields
 
     @staticmethod
-    def _build_field(name, properties: dict, required=False) -> tuple[type, dict]:
+    def _build_field(name, properties: dict, required=False) -> tuple[type, Field]:
         match properties:
             case {"anyOf": _}:
                 _field_type = "anyOf"
diff --git a/tests/parser/test_anyof_type_parser.py b/tests/parser/test_anyof_type_parser.py
index d16a3c1..b0f5220 100644
--- a/tests/parser/test_anyof_type_parser.py
+++ b/tests/parser/test_anyof_type_parser.py
@@ -7,6 +7,25 @@ from unittest import TestCase
 
 
 class TestAnyOfTypeParser(TestCase):
+    def test_any_with_missing_properties(self):
+        properties = {
+            "notAnyOf": [
+                {"type": "string"},
+                {"type": "integer"},
+            ],
+        }
+
+        with self.assertRaises(ValueError):
+            AnyOfTypeParser().from_properties("placeholder", properties)
+
+    def test_any_of_with_invalid_properties(self):
+        properties = {
+            "anyOf": None,
+        }
+
+        with self.assertRaises(ValueError):
+            AnyOfTypeParser().from_properties("placeholder", properties)
+
     def test_any_of_string_or_int(self):
         """
         Tests the AnyOfTypeParser with a string or int type.
@@ -61,3 +80,19 @@ class TestAnyOfTypeParser(TestCase):
         self.assertIn(int, get_args(type_2))
 
         self.assertEqual(type_validator["default"], 42)
+
+    def test_any_string_or_int_with_invalid_defaults(self):
+        """
+        Tests the AnyOfTypeParser with a string or int type and an invalid default value.
+        """
+
+        properties = {
+            "anyOf": [
+                {"type": "string"},
+                {"type": "integer"},
+            ],
+            "default": 3.14,
+        }
+
+        with self.assertRaises(ValueError):
+            AnyOfTypeParser().from_properties("placeholder", properties)