diff --git a/src/Umbraco.Web.BackOffice/Controllers/ContentController.cs b/src/Umbraco.Web.BackOffice/Controllers/ContentController.cs
index 845104719e..c1f08f5a85 100644
--- a/src/Umbraco.Web.BackOffice/Controllers/ContentController.cs
+++ b/src/Umbraco.Web.BackOffice/Controllers/ContentController.cs
@@ -6,6 +6,7 @@ using System.Net.Mime;
 using System.Text;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Extensions;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Logging;
@@ -606,14 +607,16 @@ namespace Umbraco.Web.BackOffice.Controllers
             return notificationModel;
         }
 
-        private void EnsureUniqueName(string name, IContent content, string modelName)
+        private bool EnsureUniqueName(string name, IContent content, string modelName)
         {
             var existing = _contentService.GetBlueprintsForContentTypes(content.ContentTypeId);
             if (existing.Any(x => x.Name == name && x.Id != content.Id))
             {
                 ModelState.AddModelError(modelName, _localizedTextService.Localize("blueprints/duplicateBlueprintMessage"));
-                throw HttpResponseException.CreateValidationErrorResponse(ModelState);
+                return false;
             }
+
+            return true;
         }
 
         /// <summary>
@@ -627,7 +630,10 @@ namespace Umbraco.Web.BackOffice.Controllers
                 contentItem,
                 content =>
                 {
-                    EnsureUniqueName(content.Name, content, "Name");
+                    if (!EnsureUniqueName(content.Name, content, "Name"))
+                    {
+                        return OperationResult.Cancel(new EventMessages());
+                    }
 
                     _contentService.SaveBlueprint(contentItem.PersistedContent, _backofficeSecurityAccessor.BackOfficeSecurity.CurrentUser.Id);
 
@@ -839,9 +845,15 @@ namespace Umbraco.Web.BackOffice.Controllers
                     v.Notifications.AddRange(n.Notifications);
             }
 
-            //lastly, if it is not valid, add the model state to the outgoing object and throw a 400
             HandleInvalidModelState(display, cultureForInvariantErrors);
 
+            //lastly, if it is not valid, add the model state to the outgoing object and throw a 400
+            if (!ModelState.IsValid)
+            {
+                display.Errors = ModelState.ToErrorDictionary();
+                return new ValidationErrorResult(display);
+            }
+
             if (wasCancelled)
             {
                 AddCancelMessage(display);
@@ -1915,9 +1927,6 @@ namespace Umbraco.Web.BackOffice.Controllers
                     AddVariantValidationError(culture, segment, "speechBubbles/contentCultureValidationError");
                 }
             }
-
-            base.HandleInvalidModelState(display);
-
         }
 
         /// <summary>
diff --git a/src/Umbraco.Web.BackOffice/Controllers/ContentTypeControllerBase.cs b/src/Umbraco.Web.BackOffice/Controllers/ContentTypeControllerBase.cs
index 965059b83f..f5934a9583 100644
--- a/src/Umbraco.Web.BackOffice/Controllers/ContentTypeControllerBase.cs
+++ b/src/Umbraco.Web.BackOffice/Controllers/ContentTypeControllerBase.cs
@@ -282,7 +282,8 @@ namespace Umbraco.Web.BackOffice.Controllers
 
             if (ModelState.IsValid == false)
             {
-                throw CreateModelStateValidationException<TContentTypeSave, TContentTypeDisplay>(ctId, contentTypeSave, ct);
+                var err = CreateModelStateValidationEror<TContentTypeSave, TContentTypeDisplay>(ctId, contentTypeSave, ct);
+                return new ValidationErrorResult(err);
             }
 
             //filter out empty properties
@@ -304,11 +305,11 @@ namespace Umbraco.Web.BackOffice.Controllers
                 catch (Exception ex)
                 {
                     var responseEx = CreateInvalidCompositionResponseException<TContentTypeDisplay, TContentTypeSave, TPropertyType>(ex, contentTypeSave, ct, ctId);
-                    if (responseEx != null) throw responseEx;
+                    if (responseEx != null) return new ValidationErrorResult(responseEx);
                 }
 
                 var exResult = CreateCompositionValidationExceptionIfInvalid<TContentTypeSave, TPropertyType, TContentTypeDisplay>(contentTypeSave, ct);
-                if (exResult != null) throw exResult;
+                if (exResult != null) return new ValidationErrorResult(exResult);
 
                 saveContentType(ct);
 
@@ -344,11 +345,14 @@ namespace Umbraco.Web.BackOffice.Controllers
                 catch (Exception ex)
                 {
                     var responseEx = CreateInvalidCompositionResponseException<TContentTypeDisplay, TContentTypeSave, TPropertyType>(ex, contentTypeSave, ct, ctId);
-                    throw responseEx ?? ex;
+                    if (responseEx is null)
+                        throw ex;
+                    
+                    return new ValidationErrorResult(responseEx);
                 }
 
                 var exResult = CreateCompositionValidationExceptionIfInvalid<TContentTypeSave, TPropertyType, TContentTypeDisplay>(contentTypeSave, newCt);
-                if (exResult != null) throw exResult;
+                if (exResult != null) return new ValidationErrorResult(exResult);
 
                 //set id to null to ensure its handled as a new type
                 contentTypeSave.Id = null;
@@ -472,7 +476,7 @@ namespace Umbraco.Web.BackOffice.Controllers
         /// <param name="contentTypeSave"></param>
         /// <param name="composition"></param>
         /// <returns></returns>
-        private HttpResponseException CreateCompositionValidationExceptionIfInvalid<TContentTypeSave, TPropertyType, TContentTypeDisplay>(TContentTypeSave contentTypeSave, TContentType composition)
+        private TContentTypeDisplay CreateCompositionValidationExceptionIfInvalid<TContentTypeSave, TPropertyType, TContentTypeDisplay>(TContentTypeSave contentTypeSave, TContentType composition)
             where TContentTypeSave : ContentTypeSave<TPropertyType>
             where TPropertyType : PropertyTypeBasic
             where TContentTypeDisplay : ContentTypeCompositionDisplay
@@ -490,7 +494,7 @@ namespace Umbraco.Web.BackOffice.Controllers
                 //map the 'save' data on top
                 display = UmbracoMapper.Map(contentTypeSave, display);
                 display.Errors = ModelState.ToErrorDictionary();
-                throw HttpResponseException.CreateValidationErrorResponse(display);
+                return display;
             }
             return null;
         }
@@ -539,7 +543,7 @@ namespace Umbraco.Web.BackOffice.Controllers
         /// <param name="ct"></param>
         /// <param name="ctId"></param>
         /// <returns></returns>
-        private HttpResponseException CreateInvalidCompositionResponseException<TContentTypeDisplay, TContentTypeSave, TPropertyType>(
+        private TContentTypeDisplay CreateInvalidCompositionResponseException<TContentTypeDisplay, TContentTypeSave, TPropertyType>(
             Exception ex, TContentTypeSave contentTypeSave, TContentType ct, int ctId)
             where TContentTypeDisplay : ContentTypeCompositionDisplay
             where TContentTypeSave : ContentTypeSave<TPropertyType>
@@ -557,7 +561,7 @@ namespace Umbraco.Web.BackOffice.Controllers
             if (invalidCompositionException != null)
             {
                 AddCompositionValidationErrors<TContentTypeSave, TPropertyType>(contentTypeSave, invalidCompositionException.PropertyTypeAliases);
-                return CreateModelStateValidationException<TContentTypeSave, TContentTypeDisplay>(ctId, contentTypeSave, ct);
+                return CreateModelStateValidationEror<TContentTypeSave, TContentTypeDisplay>(ctId, contentTypeSave, ct);
             }
             return null;
         }
@@ -570,7 +574,7 @@ namespace Umbraco.Web.BackOffice.Controllers
         /// <param name="ctId"></param>
         /// <param name="contentTypeSave"></param>
         /// <param name="ct"></param>
-        private HttpResponseException CreateModelStateValidationException<TContentTypeSave, TContentTypeDisplay>(int ctId, TContentTypeSave contentTypeSave, TContentType ct)
+        private TContentTypeDisplay CreateModelStateValidationEror<TContentTypeSave, TContentTypeDisplay>(int ctId, TContentTypeSave contentTypeSave, TContentType ct)
             where TContentTypeDisplay : ContentTypeCompositionDisplay
             where TContentTypeSave : ContentTypeSave
         {
@@ -589,7 +593,7 @@ namespace Umbraco.Web.BackOffice.Controllers
             }
 
             forDisplay.Errors = ModelState.ToErrorDictionary();
-            return HttpResponseException.CreateValidationErrorResponse(forDisplay);
+            return forDisplay;
         }
     }
 }