diff --git a/DbFirst.API/Middleware/ExceptionHandlingMiddleware.cs b/DbFirst.API/Middleware/ExceptionHandlingMiddleware.cs
index 4957a94..369ed1b 100644
--- a/DbFirst.API/Middleware/ExceptionHandlingMiddleware.cs
+++ b/DbFirst.API/Middleware/ExceptionHandlingMiddleware.cs
@@ -1,5 +1,4 @@
-using System.Net;
-using System.Text.Json;
+using Microsoft.AspNetCore.Mvc;
 
 namespace DbFirst.API.Middleware;
 
@@ -20,33 +19,35 @@ public class ExceptionHandlingMiddleware
         {
             await _next(context);
         }
+        catch (InvalidOperationException ex)
+        {
+            _logger.LogWarning(ex, "Domain validation error");
+            await WriteProblemAsync(context, StatusCodes.Status400BadRequest, "Eingabe ungültig", ex.Message);
+        }
         catch (Exception ex)
         {
             _logger.LogError(ex, "Unhandled exception");
-            await WriteProblemDetailsAsync(context, ex);
+            await WriteProblemAsync(context, StatusCodes.Status500InternalServerError, "Serverfehler", ex.Message);
         }
     }
 
-    private static async Task WriteProblemDetailsAsync(HttpContext context, Exception ex)
+    private static async Task WriteProblemAsync(HttpContext context, int status, string title, string detail)
     {
-        if (context.Response.HasStarted)
-        {
-            throw ex;
-        }
+        if (context.Response.HasStarted) return;
 
         context.Response.Clear();
-        context.Response.StatusCode = (int)HttpStatusCode.InternalServerError;
-        context.Response.ContentType = "application/json";
+        context.Response.StatusCode = status;
+        context.Response.ContentType = "application/problem+json";
 
-        var problem = new
+        var problem = new ProblemDetails
         {
-            type = "https://tools.ietf.org/html/rfc9110#section-15.6.1",
-            title = "Serverfehler",
-            status = context.Response.StatusCode,
-            detail = ex.Message,
-            traceId = context.TraceIdentifier
+            Type = $"https://tools.ietf.org/html/rfc9110#section-{(status == 400 ? "15.5.1" : "15.6.1")}",
+            Title = title,
+            Status = status,
+            Detail = detail,
+            Extensions = { ["traceId"] = context.TraceIdentifier }
         };
 
-        await context.Response.WriteAsync(JsonSerializer.Serialize(problem));
+        await context.Response.WriteAsJsonAsync(problem);
     }
 }
diff --git a/DbFirst.API/Program.cs b/DbFirst.API/Program.cs
index 3fd04b7..2ae820a 100644
--- a/DbFirst.API/Program.cs
+++ b/DbFirst.API/Program.cs
@@ -13,6 +13,7 @@ var builder = WebApplication.CreateBuilder(args);
 builder.Services.AddControllers();
 builder.Services.AddEndpointsApiExplorer();
 builder.Services.AddSwaggerGen();
+builder.Services.AddProblemDetails();
 
 // TODO: allow listed origins configured in appsettings.json
 // In any case, dont let them to free to use without cors. if there is no origin specified, block all.