fast.diff

diff --git a/lib/Mojo/Headers.pm b/lib/Mojo/Headers.pm
index 320d4a4..1004eee 100644
--- a/lib/Mojo/Headers.pm
+++ b/lib/Mojo/Headers.pm
@@ -20,9 +20,20 @@ my %NORMALCASE = map { lc() => $_ } (
   qw(Upgrade User-Agent Vary WWW-Authenticate)
 );
 for my $header (values %NORMALCASE) {
-  my $name = lc $header;
+  my $name = my $key = lc $header;
   $name =~ y/-/_/;
-  monkey_patch __PACKAGE__, $name, sub { shift->header($header => @_) };
+  monkey_patch __PACKAGE__, $name, sub {
+    my $self = shift;
+
+    unless (@_) {
+      return undef unless my $headers = $self->{headers}{$key};
+      return join ', ', @$headers;
+    }
+
+    $self->{normalcase}{$key} //= $name unless $NORMALCASE{$key};
+    $self->{headers}{$key} = [@_];
+    return $self;
+  };
 }
 
 sub add {