diff --git a/lib/PDL/Stats/TS.pd b/lib/PDL/Stats/TS.pd
index 3bb1386..82ce1d7 100644
--- a/lib/PDL/Stats/TS.pd
+++ b/lib/PDL/Stats/TS.pd
@@ -48,8 +48,9 @@ pp_addhdr('
 );
 
 pp_def('acf',
-  Pars  => 'x(t); [o]r(h)',
-  OtherPars => 'IV lag=>h',
+  Pars  => 'x(t); [o]r(h=CALC($COMP(lag) < 0 ? $SIZE(t) : $COMP(lag) + 1))',
+  OtherPars => 'IV lag',
+  OtherParsDefaults => { lag => -1 },
   GenericTypes => $F,
   Code  => '
 $GENERIC(x) s, s2, m, cov0, covh;
@@ -75,14 +76,6 @@ loop (h) %{
   }
 %}
 ',
-  PMCode => pp_line_numbers(__LINE__, <<'EOF'),
-sub PDL::acf {
-  my ($self, $h) = @_;
-  $h ||= $self->dim(0) - 1;
-  PDL::_acf_int($self, my $r = PDL->null, $h+1);
-  $r;
-}
-EOF
  Doc => <<'EOD',
 =for ref
 
@@ -104,8 +97,9 @@ EOD
 );
 
 pp_def('acvf',
-  Pars  => 'x(t); [o]v(h)',
-  OtherPars => 'IV lag=>h;',
+  Pars  => 'x(t); [o]v(h=CALC($COMP(lag) < 0 ? $SIZE(t) : $COMP(lag) + 1))',
+  OtherPars => 'IV lag',
+  OtherParsDefaults => { lag => -1 },
   GenericTypes => $F,
   Code  => '
 $GENERIC(x) s, s2, m, covh;
@@ -130,14 +124,6 @@ loop (h) %{
   }
 %}
 ',
-  PMCode => pp_line_numbers(__LINE__, <<'EOF'),
-sub PDL::acvf {
-  my ($self, $h) = @_;
-  $h ||= $self->dim(0) - 1;
-  PDL::_acvf_int($self, my $v = PDL->null, $h+1);
-  $v;
-}
-EOF
  Doc => <<'EOD',
 =for ref
 
diff --git a/t/ts.t b/t/ts.t
index d3fc97a..5a64881 100644
--- a/t/ts.t
+++ b/t/ts.t
@@ -58,4 +58,25 @@ use Test::PDL;
   is_pdl $ms, $ans_ms, 'season_m ms';
 }
 
+subtest 'acf and acvf with lags' => sub {
+  my $a = sequence 10;
+  my $m = sequence 10,2;
+  my $acvf = pdl '[82.5 57.75 34 12.25 -6.5 -21.25 -31 -34.75 -31.5 -20.25]';
+  my $acf  = $acvf / $acvf->at(0);
+
+  is_pdl $a->acvf(), $acvf, "calculate autocovariance with no arguments on $a";
+
+  is_pdl $a->acvf(4), $acvf->slice('0:4'), "calculate autocovariance with 4 lags on $a";
+  is_pdl $a->acvf(0), $acvf->slice('0:0'), "calculate autocovariance with 0 lag on $a";
+  is_pdl $a->acvf(5) / $a->acvf(0), $a->acf(5), "calculate autocorrelation from autocovariance on $a";
+  is_pdl $a->acvf(14), $acvf->append([0,0,0,0,0]), "autocovariance called with more lags than values";
+
+  is_pdl $a->acf(), $acf, "calculate autocorrelation with no arguments on $a";
+  is_pdl $a->acf(0), pdl('[1]'), 'first value of the autocorrelation function is always 1';
+  is_pdl $a->acf(5), $acf->slice('0:5'), 'autocorrelation function with 5 lags';
+
+  # autocorrelation on higher order pdls is a collection of 1D arrays
+  is_pdl $m->acvf(4), $acvf->slice('0:4')->dummy(1,2), "acvf is the same for both rows of sequence(10,2)";
+};
+
 done_testing;