diff --git a/Netkan/Transformers/DownloadAttributeTransformer.cs b/Netkan/Transformers/DownloadAttributeTransformer.cs
index 8e2f79d2c..c0ba9226e 100644
--- a/Netkan/Transformers/DownloadAttributeTransformer.cs
+++ b/Netkan/Transformers/DownloadAttributeTransformer.cs
@@ -58,7 +58,7 @@ public IEnumerable<Metadata> Transform(Metadata metadata, TransformOptions? opts
                     json["download_hash"] = download_hashJson;
 
                     Log.Debug("Calculating download MIME type...");
-                    json["download_content_type"] = _fileService.GetMimetype(file);
+                    json.SafeAdd("download_content_type", _fileService.GetMimetype(file));
                 }
 
                 Log.DebugFormat("Transformed metadata:{0}{1}", Environment.NewLine, json);