diff --git a/osu.Game/Beatmaps/Formats/Decoder.cs b/osu.Game/Beatmaps/Formats/Decoder.cs
index 2927654f62..759d6d14d1 100644
--- a/osu.Game/Beatmaps/Formats/Decoder.cs
+++ b/osu.Game/Beatmaps/Formats/Decoder.cs
@@ -55,11 +55,11 @@ namespace osu.Game.Beatmaps.Formats
             } while (line != null && line.Length == 0);
 
             if (line == null)
-                throw new IOException(@"Unknown file format");
+                throw new IOException(@"Unknown file format (null)");
 
             var decoder = typedDecoders.Select(d => line.StartsWith(d.Key) ? d.Value : null).FirstOrDefault();
             if (decoder == null)
-                throw new IOException(@"Unknown file format");
+                throw new IOException($@"Unknown file format ({line})");
 
             return (Decoder<T>)decoder.Invoke(line);
         }