diff --git a/tests/test_json_model.py b/tests/test_json_model.py
index 4d79565..847239c 100644
--- a/tests/test_json_model.py
+++ b/tests/test_json_model.py
@@ -48,7 +48,7 @@ class Member(BaseJsonModel):
     last_name: str
     email: str = Field(index=True)
     join_date: datetime.date
-    age: int
+    age: int = Field(index=True)
 
     # Creates an embedded model.
     address: Address