diff --git a/lib/Subtitle/SSA/Style.pm b/lib/Subtitle/SSA/Style.pm
index 7b57869..70208a8 100644
--- a/lib/Subtitle/SSA/Style.pm
+++ b/lib/Subtitle/SSA/Style.pm
@@ -81,15 +81,19 @@ sub to_string {
   my ($self) = @_;
   my @fields = $self->fields();
   my $string = "Style: ";
+  my @values = ();
   foreach my $field (@fields) {
     my $d = $STYLE_DEFAULTS{$field};
+    my $v = $self->{$f} // $d->{value};
     if ($d->{type} eq 'x') {
       $fmt = ($self->{_vers} eq 'ass') ? '&H%08X' : '%d';
-      $string .= sprintf $fmt, $self->{$f};
+      $v = sprintf $fmt, $v;
     } else {
-      $string .= $self->{$f} // $d->{value};
+      # use as is
     }
+    push @values, $v;
   }
+  $string .= join(',', @values);
 
   return $string;
 }