diff --git a/lib/Magnum/Schema/ResultSet/InvoiceLine.pm b/lib/Magnum/Schema/ResultSet/InvoiceLine.pm
index c4e2133..7ffc759 100644
--- a/lib/Magnum/Schema/ResultSet/InvoiceLine.pm
+++ b/lib/Magnum/Schema/ResultSet/InvoiceLine.pm
@@ -2,12 +2,24 @@ package Magnum::Schema::ResultSet::InvoiceLine;
 
 use strict;
 use warnings;
-use base 'DBIx::Class::ResultSet';
+use Moose;
+use MooseX::NonMoose;
+extends 'DBIx::Class::ResultSet';
+
+sub BUILDARGS { $_[2] }
+
+has default_vat_type => (
+  is => 'ro',
+  isa => 'Str',
+  default => 'standard',
+);
 
 sub filter_by_vat_type {
   my $self = shift;
   my ($vat_type) = @_;
 
+  $vat_type //= $self->default_vat_type;
+
   $self->search({
     vat => $vat_type,
   });
diff --git a/lib/Magnum/Schema/ResultSet/VatRate.pm b/lib/Magnum/Schema/ResultSet/VatRate.pm
index aa89d7b..d296e1e 100644
--- a/lib/Magnum/Schema/ResultSet/VatRate.pm
+++ b/lib/Magnum/Schema/ResultSet/VatRate.pm
@@ -2,7 +2,20 @@ package Magnum::Schema::ResultSet::VatRate;
 
 use strict;
 use warnings;
-use base 'DBIx::Class::ResultSet';
+use Moose;
+use MooseX::NonMoose;
+extends 'DBIx::Class::ResultSet';
+
+sub BUILDARGS { $_[2] }
+
+has datetime_formatter => (
+  is => 'ro',
+  lazy_build => 1,
+);
+
+sub _build_datetime_formatter {
+  return $_[0]->result_source->schema->storage->datetime_parser;
+}
 
 sub vat_rate_for_date {
   my $self = shift;
@@ -10,8 +23,7 @@ sub vat_rate_for_date {
 
   $type //= 'standard';
 
-  my $dtf = $self->result_source->schema->storage->datetime_parser;
-  my $search_date = $dtf->format_datetime($date);
+  my $search_date = $self->datetime_formatter->format_datetime($date);
 
   my ($rate) = $self->search({
     type => $type,