diff --git a/lib/plum/rack/session.rb b/lib/plum/rack/session.rb
index <HASH>..<HASH> 100644
--- a/lib/plum/rack/session.rb
+++ b/lib/plum/rack/session.rb
@@ -195,7 +195,6 @@ module Plum
             if "set-cookie" == key
               rbase[key] = v_.gsub("\n", "; ") # RFC 7540 8.1.2.5
             elsif !INVALID_HEADERS.member?(key)
-              key.byteshift(2) if key.start_with?("x-")
               rbase[key] = v_.tr("\n", ",") # RFC 7230 7
             end
           end
rack/session: don't remove x-