diff --git a/src/Umbraco.Core/Builder/UmbracoBuilder.cs b/src/Umbraco.Core/Builder/UmbracoBuilder.cs
index b167f1694f..2a5c93b0d7 100644
--- a/src/Umbraco.Core/Builder/UmbracoBuilder.cs
+++ b/src/Umbraco.Core/Builder/UmbracoBuilder.cs
@@ -1,13 +1,12 @@
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
-using System;
-using System.Collections.Generic;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
+using System;
+using System.Collections.Generic;
 using Umbraco.Core.Builder;
 using Umbraco.Core.Composing;
 using Umbraco.Core.Events;
-using Microsoft.Extensions.DependencyInjection.Extensions;
 
 namespace Umbraco.Web.Common.Builder
 {
@@ -62,13 +61,9 @@ namespace Umbraco.Web.Common.Builder
 
         private void AddCoreServices()
         {
-            // TODO: Should this be an explicit public method accepting a service lifetime?
-            // Register the aggregator and factory as transient.
-            // Use TryAdd to allow simple refactoring to allow additional registrations.
-            // Transiant registration matches the default registration of Mediatr and
-            // should encourage the avoidance of singletons throughout the codebase.
-            Services.TryAddTransient<ServiceFactory>(p => p.GetService);
-            Services.TryAdd(new ServiceDescriptor(typeof(IEventAggregator), typeof(EventAggregator), ServiceLifetime.Transient));
+            // Register as singleton to allow injection everywhere.
+            Services.AddSingleton<ServiceFactory>(p => p.GetService);
+            Services.AddSingleton<IEventAggregator, EventAggregator>();
         }
     }
 }
diff --git a/src/Umbraco.Tests.UnitTests/Umbraco.Core/Events/EventAggregatorTests.cs b/src/Umbraco.Tests.UnitTests/Umbraco.Core/Events/EventAggregatorTests.cs
index c89fa2f9fd..9c1fd87974 100644
--- a/src/Umbraco.Tests.UnitTests/Umbraco.Core/Events/EventAggregatorTests.cs
+++ b/src/Umbraco.Tests.UnitTests/Umbraco.Core/Events/EventAggregatorTests.cs
@@ -28,6 +28,7 @@ namespace Umbraco.Tests.UnitTests.Umbraco.Core.Events
         [Test]
         public async Task CanPublishEvents()
         {
+            _builder.Services.AddScoped<Adder>();
             _builder.AddNotificationHandler<Notification, NotificationHandlerA>();
             _builder.AddNotificationHandler<Notification, NotificationHandlerB>();
             _builder.AddNotificationHandler<Notification, NotificationHandlerC>();
@@ -65,11 +66,23 @@ namespace Umbraco.Tests.UnitTests.Umbraco.Core.Events
 
         public class NotificationHandlerC : INotificationHandler<Notification>
         {
+            private readonly Adder _adder;
+
+            public NotificationHandlerC(Adder adder) => _adder = adder;
+
             public Task HandleAsync(Notification notification, CancellationToken cancellationToken)
             {
-                notification.SubscriberCount += C;
+                notification.SubscriberCount = _adder.Add(notification.SubscriberCount, C);
                 return Task.CompletedTask;
             }
         }
+
+        public class Adder
+        {
+            public int Add(int a, int b)
+            {
+                return a + b;
+            }
+        }
     }
 }