diff --git a/dist/ExtUtils-ParseXS/lib/ExtUtils/ParseXS.pm b/dist/ExtUtils-ParseXS/lib/ExtUtils/ParseXS.pm
index 0987500..dd1c3f2 100644
--- a/dist/ExtUtils-ParseXS/lib/ExtUtils/ParseXS.pm
+++ b/dist/ExtUtils-ParseXS/lib/ExtUtils/ParseXS.pm
@@ -686,7 +686,7 @@ EOF
         var         => $_,
         do_setmagic => $self->{DoSetMagic},
         do_push     => undef,
-      } ) for grep $self->{in_out}->{$_} =~ /OUT$/, keys %{ $self->{in_out} };
+      } ) for grep $self->{in_out}->{$_} =~ /OUT$/, sort keys %{ $self->{in_out} };
 
       my $prepush_done;
       # all OUTPUT done, so now push the return value on the stack