diff --git a/Sandreas.AudioMetadata/AudioMetadata/MetadataTrack.cs b/Sandreas.AudioMetadata/AudioMetadata/MetadataTrack.cs
index 5bcf807..68e40a7 100644
--- a/Sandreas.AudioMetadata/AudioMetadata/MetadataTrack.cs
+++ b/Sandreas.AudioMetadata/AudioMetadata/MetadataTrack.cs
@@ -39,7 +39,7 @@ public MetadataTrack(IFileSystemInfo fileInfo, bool load = true)
         { nameof(Subtitle), ("TIT3", "TIT3", "----:com.apple.iTunes:SUBTITLE", "T=30", "WM/SubTitle", "Subtitle", "SUBTITLE", "") },
         /*mp4 => ©st3 ? */
     };
-    protected IDictionary<string, string> MapAdditionalFields()
+    protected override IDictionary<string, string> MapAdditionalFields()
     {
         return AdditionalFields
             .Where(kvp =>
diff --git a/Sandreas.AudioMetadata/AudioMetadata/MetadataTrackHolder.cs b/Sandreas.AudioMetadata/AudioMetadata/MetadataTrackHolder.cs
index a389470..57e9339 100644
--- a/Sandreas.AudioMetadata/AudioMetadata/MetadataTrackHolder.cs
+++ b/Sandreas.AudioMetadata/AudioMetadata/MetadataTrackHolder.cs
@@ -28,7 +28,7 @@ public TimeSpan TotalDuration
     }
 
     public IDictionary<string, string> MappedAdditionalFields => MapAdditionalFields();
-    private IDictionary<string, string> MapAdditionalFields() => AdditionalFields;
+    protected virtual IDictionary<string, string> MapAdditionalFields() => AdditionalFields;
 
     public int? Bpm
     {