diff --git a/Controllers/APIController.cs b/Controllers/APIController.cs
index 068e787..a5fd82d 100644
--- a/Controllers/APIController.cs
+++ b/Controllers/APIController.cs
@@ -120,7 +120,14 @@ namespace CarCareTracker.Controllers
             {
                 result = _userLogic.FilterUserVehicles(result, GetUserID());
             }
-            return Json(result);
+            if (_config.GetInvariantApi() || Request.Headers.ContainsKey("culture-invariant"))
+            {
+                return Json(result, StaticHelper.GetInvariantOption());
+            }
+            else
+            {
+                return Json(result);
+            }
         }
 
         [HttpGet]
diff --git a/Models/Vehicle.cs b/Models/Vehicle.cs
index 6b45d21..6f2ccb1 100644
--- a/Models/Vehicle.cs
+++ b/Models/Vehicle.cs
@@ -1,4 +1,6 @@
-namespace CarCareTracker.Models
+using System.Text.Json.Serialization;
+
+namespace CarCareTracker.Models
 {
     public class Vehicle
     {
@@ -8,7 +10,9 @@
         public string Make { get; set; }
         public string Model { get; set; }
         public string LicensePlate { get; set; }
+        [JsonConverter(typeof(FromDateOptional))]
         public string PurchaseDate { get; set; }
+        [JsonConverter(typeof(FromDateOptional))]
         public string SoldDate { get; set; }
         public decimal PurchasePrice { get; set; }
         public decimal SoldPrice { get; set; }