diff --git a/src/Ocelot/DependencyInjection/OcelotBuilder.cs b/src/Ocelot/DependencyInjection/OcelotBuilder.cs
index 77f29c5a..94ca903c 100644
--- a/src/Ocelot/DependencyInjection/OcelotBuilder.cs
+++ b/src/Ocelot/DependencyInjection/OcelotBuilder.cs
@@ -55,16 +55,16 @@ namespace Ocelot.DependencyInjection
             Services.TryAddSingleton<IInternalConfigurationCreator, FileInternalConfigurationCreator>();
             Services.TryAddSingleton<IInternalConfigurationRepository, InMemoryInternalConfigurationRepository>();
             Services.TryAddSingleton<IConfigurationValidator, FileConfigurationFluentValidator>();
-            Services.AddSingleton<HostAndPortValidator>();
-            Services.AddSingleton<IReRoutesCreator, ReRoutesCreator>();
-            Services.AddSingleton<IAggregatesCreator, AggregatesCreator>();
-            Services.AddSingleton<IReRouteKeyCreator, ReRouteKeyCreator>();
-            Services.AddSingleton<IConfigurationCreator, ConfigurationCreator>();
-            Services.AddSingleton<IDynamicsCreator, DynamicsCreator>();
-            Services.AddSingleton<ILoadBalancerOptionsCreator, LoadBalancerOptionsCreator>();
-            Services.AddSingleton<ReRouteFluentValidator>();
-            Services.AddSingleton<FileGlobalConfigurationFluentValidator>();
-            Services.AddSingleton<FileQoSOptionsFluentValidator>();
+            Services.TryAddSingleton<HostAndPortValidator>();
+            Services.TryAddSingleton<IReRoutesCreator, ReRoutesCreator>();
+            Services.TryAddSingleton<IAggregatesCreator, AggregatesCreator>();
+            Services.TryAddSingleton<IReRouteKeyCreator, ReRouteKeyCreator>();
+            Services.TryAddSingleton<IConfigurationCreator, ConfigurationCreator>();
+            Services.TryAddSingleton<IDynamicsCreator, DynamicsCreator>();
+            Services.TryAddSingleton<ILoadBalancerOptionsCreator, LoadBalancerOptionsCreator>();
+            Services.TryAddSingleton<ReRouteFluentValidator>();
+            Services.TryAddSingleton<FileGlobalConfigurationFluentValidator>();
+            Services.TryAddSingleton<FileQoSOptionsFluentValidator>();
             Services.TryAddSingleton<IClaimsToThingCreator, ClaimsToThingCreator>();
             Services.TryAddSingleton<IAuthenticationOptionsCreator, AuthenticationOptionsCreator>();
             Services.TryAddSingleton<IUpstreamTemplatePatternCreator, UpstreamTemplatePatternCreator>();
@@ -92,8 +92,8 @@ namespace Ocelot.DependencyInjection
             Services.TryAddSingleton<IUrlPathToUrlTemplateMatcher, RegExUrlMatcher>();
             Services.TryAddSingleton<IPlaceholderNameAndValueFinder, UrlPathPlaceholderNameAndValueFinder>();
             Services.TryAddSingleton<IDownstreamPathPlaceholderReplacer, DownstreamTemplatePathPlaceholderReplacer>();
-            Services.AddSingleton<IDownstreamRouteProvider, DownstreamRouteFinder>();
-            Services.AddSingleton<IDownstreamRouteProvider, DownstreamRouteCreator>();
+            Services.TryAddSingleton<IDownstreamRouteProvider, DownstreamRouteFinder>();
+            Services.TryAddSingleton<IDownstreamRouteProvider, DownstreamRouteCreator>();
             Services.TryAddSingleton<IDownstreamRouteProviderFactory, DownstreamRouteProviderFactory>();
             Services.TryAddSingleton<IHttpRequester, HttpClientHttpRequester>();
             Services.TryAddSingleton<IHttpResponder, HttpContextResponder>();
@@ -114,7 +114,7 @@ namespace Ocelot.DependencyInjection
             Services.TryAddSingleton<OcelotDiagnosticListener>();
             Services.TryAddSingleton<IMultiplexer, Multiplexer>();
             Services.TryAddSingleton<IResponseAggregator, SimpleJsonResponseAggregator>();
-            Services.AddSingleton<ITracingHandlerFactory, TracingHandlerFactory>();
+            Services.TryAddSingleton<ITracingHandlerFactory, TracingHandlerFactory>();
             Services.TryAddSingleton<IFileConfigurationPollerOptions, InMemoryFileConfigurationPollerOptions>();
             Services.TryAddSingleton<IAddHeadersToResponse, AddHeadersToResponse>();
             Services.TryAddSingleton<IPlaceholders, Placeholders>();
diff --git a/src/Ocelot/Responder/HttpContextResponder.cs b/src/Ocelot/Responder/HttpContextResponder.cs
index 1b20992d..0e964c7a 100644
--- a/src/Ocelot/Responder/HttpContextResponder.cs
+++ b/src/Ocelot/Responder/HttpContextResponder.cs
@@ -44,7 +44,7 @@ namespace Ocelot.Responder
                 AddHeaderIfDoesntExist(context, new Header("Content-Length", new []{ response.Content.Headers.ContentLength.ToString() }) );
             }
 
-            context.Response.StatusCode = (int)response.StatusCode;
+            SetStatusCode(context, (int)response.StatusCode);
 
             context.Response.HttpContext.Features.Get<IHttpResponseFeature>().ReasonPhrase = response.ReasonPhrase;
 
@@ -59,7 +59,15 @@ namespace Ocelot.Responder
 
         public void SetErrorResponseOnContext(HttpContext context, int statusCode)
         {
-            context.Response.StatusCode = statusCode;
+            SetStatusCode(context, statusCode);
+        }
+
+        private void SetStatusCode(HttpContext context, int statusCode)
+        {
+            if (!context.Response.HasStarted)
+            {
+                context.Response.StatusCode = statusCode;
+            }
         }
 
         private static void AddHeaderIfDoesntExist(HttpContext context, Header httpResponseHeader)