Index: lib/webrick/httpservlet/filehandler.rb
===================================================================
--- lib/webrick/httpservlet/filehandler.rb	(revision 26281)
+++ lib/webrick/httpservlet/filehandler.rb	(working copy)
@@ -107,7 +107,7 @@
               content = io.read(last-first+1)
             end
             res['content-type'] = mtype
-            res['content-range'] = "#{first}-#{last}/#{filesize}"
+            res['content-range'] = "bytes #{first}-#{last}/#{filesize}"
             res['content-length'] = last - first + 1
             res.body = content
           else