diff --git a/lib/webvtt.rb b/lib/webvtt.rb
index f8c6c63..9a991ac 100644
--- a/lib/webvtt.rb
+++ b/lib/webvtt.rb
@@ -3,6 +3,7 @@
 
 module Webvtt
   # Your code goes here...
+  class MalformedError < StandardError; end
 end
 
 require 'webvtt/file'
diff --git a/lib/webvtt/file.rb b/lib/webvtt/file.rb
index 10706b1..545e4e5 100644
--- a/lib/webvtt/file.rb
+++ b/lib/webvtt/file.rb
@@ -25,7 +25,7 @@ def initialize(input_file)
     def parse
       remove_bom
       if !webvtt_line?(file.lines.first)
-        raise Webvtt::MalformedError
+        raise Webvtt::MalformedError, "Invalid WebVTT file format"
       end
       in_header = true
       collected_lines = []