diff --git a/src/Umbraco.Web.BackOffice/Controllers/DetermineAmbiguousActionByPassingParameters.cs b/src/Umbraco.Web.BackOffice/Controllers/DetermineAmbiguousActionByPassingParameters.cs
index a6432402b4..fc6c3b6814 100644
--- a/src/Umbraco.Web.BackOffice/Controllers/DetermineAmbiguousActionByPassingParameters.cs
+++ b/src/Umbraco.Web.BackOffice/Controllers/DetermineAmbiguousActionByPassingParameters.cs
@@ -3,15 +3,16 @@ using System.Collections;
 using System.Collections.Generic;
 using System.Linq;
 using System.Net.Http;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.ActionConstraints;
 using Microsoft.AspNetCore.Routing;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
 using Umbraco.Core;
 using Umbraco.Extensions;
 using Umbraco.Web.BackOffice.ModelBinders;
-using Microsoft.AspNetCore.Http;
-using Newtonsoft.Json;
-using Newtonsoft.Json.Linq;
 
 namespace Umbraco.Web.BackOffice.Controllers
 {
@@ -102,7 +103,11 @@ namespace Umbraco.Web.BackOffice.Controllers
                 // IMPORTANT: Ensure the requestBody can be read multiple times.
                 routeContext.HttpContext.Request.EnableBuffering();
 
-                var body = _requestBody ??= routeContext.HttpContext.Request.GetRawBodyString();
+                // We need to use the asynchronous method here if synchronous IO is not allowed (it may or may not be, depending
+                // on configuration in UmbracoBackOfficeServiceCollectionExtensions.AddUmbraco()).
+                // We can't use async/await due to the need to override IsValidForRequest, which doesn't have an async override, so going with
+                // this, which seems to be the least worst option for "sync to async" (https://stackoverflow.com/a/32429753/489433).
+                var body = _requestBody ??= Task.Run(() => routeContext.HttpContext.Request.GetRawBodyStringAsync()).GetAwaiter().GetResult();
 
                 var jToken = JsonConvert.DeserializeObject<JToken>(body);
 
diff --git a/src/Umbraco.Web.BackOffice/Extensions/BackOfficeServiceCollectionExtensions.cs b/src/Umbraco.Web.BackOffice/Extensions/BackOfficeServiceCollectionExtensions.cs
index 8ca1de2987..d30db016e7 100644
--- a/src/Umbraco.Web.BackOffice/Extensions/BackOfficeServiceCollectionExtensions.cs
+++ b/src/Umbraco.Web.BackOffice/Extensions/BackOfficeServiceCollectionExtensions.cs
@@ -1,17 +1,9 @@
-using System;
-using System.Reflection;
-using Microsoft.AspNetCore.Builder;
-using Microsoft.AspNetCore.Hosting;
-using Microsoft.AspNetCore.Identity;
+using Microsoft.AspNetCore.Identity;
 using Microsoft.AspNetCore.Mvc.Filters;
-using Microsoft.AspNetCore.Server.Kestrel.Core;
-using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;
-using Microsoft.Extensions.Options;
 using Umbraco.Core;
 using Umbraco.Core.BackOffice;
-using Umbraco.Core.Configuration.Models;
 using Umbraco.Core.Security;
 using Umbraco.Core.Serialization;
 using Umbraco.Infrastructure.BackOffice;
@@ -23,7 +15,6 @@ using Umbraco.Web.Common.Security;
 
 namespace Umbraco.Extensions
 {
-
     public static class BackOfficeServiceCollectionExtensions
     {
         /// <summary>
diff --git a/src/Umbraco.Web.Common/Extensions/HttpRequestExtensions.cs b/src/Umbraco.Web.Common/Extensions/HttpRequestExtensions.cs
index 0369717b9b..69fae56d32 100644
--- a/src/Umbraco.Web.Common/Extensions/HttpRequestExtensions.cs
+++ b/src/Umbraco.Web.Common/Extensions/HttpRequestExtensions.cs
@@ -79,8 +79,6 @@ namespace Umbraco.Extensions
                 request.Body.Seek(0, SeekOrigin.Begin);
                 return result;
             }
-
-
         }
 
         public static async Task<string> GetRawBodyStringAsync(this HttpRequest request, Encoding encoding = null)