diff --git a/app/models/dmsf_file.rb b/app/models/dmsf_file.rb
index bc5a91d3..d802220d 100644
--- a/app/models/dmsf_file.rb
+++ b/app/models/dmsf_file.rb
@@ -507,7 +507,7 @@ class DmsfFile < ActiveRecord::Base
   end
 
   def extension
-    $1 if self.last_revision && self.last_revision.disk_filename =~ /\.(.+)$/
+    File.extname(self.last_revision.disk_filename).strip.downcase[1..-1] if self.last_revision
   end
 
   include ActionView::Helpers::NumberHelper