diff --git a/src/JsonApiDotNetCore/Middleware/JsonApiMiddleware.cs b/src/JsonApiDotNetCore/Middleware/JsonApiMiddleware.cs
index fee92a14dc..84d861ab26 100644
--- a/src/JsonApiDotNetCore/Middleware/JsonApiMiddleware.cs
+++ b/src/JsonApiDotNetCore/Middleware/JsonApiMiddleware.cs
@@ -140,6 +140,7 @@ private static async Task<bool> ValidateAcceptHeaderAsync(HttpContext httpContex
 
         private static async Task FlushResponseAsync(HttpResponse httpResponse, JsonSerializerSettings serializerSettings, Error error)
         {
+            httpResponse.ContentType = HeaderConstants.MediaType;
             httpResponse.StatusCode = (int) error.StatusCode;
 
             JsonSerializer serializer = JsonSerializer.CreateDefault(serializerSettings);