diff --git a/lib/PDL/Slices.pd b/lib/PDL/Slices.pd
index 9dfe2b52f..07f3672e3 100644
--- a/lib/PDL/Slices.pd
+++ b/lib/PDL/Slices.pd
@@ -1186,7 +1186,8 @@ pp_def('rldvec',
   PMCode =>pp_line_numbers(__LINE__, <<'EOC'),
 sub PDL::rldvec {
   my ($a,$b,$c) = @_;
-  ($c,my $sm) = defined($c) ? ($c,$c->dim(1)) : (PDL->null,$a->sumover->max->sclr);
+  $c = PDL->null unless defined $c;
+  my $sm = $c->isnull ? $a->sumover->max->sclr : $c->dim(1);
   PDL::_rldvec_int($a,$b,$c,$sm);
   return $c;
 }
@@ -1209,6 +1210,9 @@ of row-vectors each of length $M, run-length decode to $c().
 
 Can be used together with clump() to run-length decode "values" of arbitrary dimensions.
 
+Note: $sumover_max is used internally only. Any value provided will be
+ignored.
+
 See also: L</rld>.
 Contributed by Bryan Jurish E<lt>moocow@cpan.orgE<gt>.
 EOD
@@ -1257,7 +1261,8 @@ pp_def('rldseq',
   PMCode =>pp_line_numbers(__LINE__, <<'EOC'),
 sub PDL::rldseq {
   my ($a,$b,$c) = @_;
-  ($c,my $sm) = defined($c) ? ($c,$c->dim(1)) : (PDL->null,$a->sumover->max->sclr);
+  $c = PDL->null unless defined $c;
+  my $sm = $c->isnull ? $a->sumover->max->sclr : $c->dim(1);
   PDL::_rldseq_int($a,$b,$c,$sm);
   return $c;
 }
@@ -1283,6 +1288,9 @@ as for:
  $c = null;
  $c = $c->append($b($_)+sequence($a->type,$a($_))) foreach (0..($N-1));
 
+Note: $sumover_max is used internally only. Any value provided will be
+ignored.
+
 See also: L</rld>.
 Contributed by Bryan Jurish E<lt>moocow@cpan.orgE<gt>.
 EOD
@@ -1352,19 +1360,21 @@ sub rldND {
   my ($counts,$elts) = (shift,shift);
   my @vdimsN        = $elts->dims;
 
-  ##-- construct output pdl
-  my ($data);
-  if ($#_ >= 0) { $data = $_[0]; }
-  else {
-    my $size      = $counts->sumover->max; ##-- get maximum size for Nth-dimension for small encodings
-    my @countdims = $counts->dims;
-    shift(@countdims);
-    $data         = zeroes($elts->type, @vdimsN, @countdims);
-  }
+  ##-- allocate output pdl if none given
+  my $data = @_ ? $_[0] : PDL->null;
+  my $have_null = $data->isnull;
 
   ##-- guts: call rldvec()
-  rldvec($counts, $elts->clump($#vdimsN), $data->clump($#vdimsN));
-
+  rldvec($counts, $elts->clump($#vdimsN),
+    $have_null ? $data : $data->clump($#vdimsN));
+
+  ##-- reshape output according to $elts
+  if ($have_null) {
+    my @dims = $data->dims;
+    pop(@vdimsN);
+    splice(@dims, 0, 1, @vdimsN);
+    $data->reshape(@dims);
+  }
   return $data;
 }
 EOF
diff --git a/t/slice.t b/t/slice.t
index 7a4c42fbc..871d3df16 100644
--- a/t/slice.t
+++ b/t/slice.t
@@ -404,6 +404,11 @@ is_pdl $pv, my $pv_expect = pdl([[1,2],[3,4],[5,6],[0,0],[0,0],[0,0]]), "rlevec(
 
 my $pd = rldvec($pf,$pv);
 is_pdl $pd, $p, "rldvec()";
+rldvec($pf,$pv,my $pdn = null);
+is_pdl $pdn, $p, "rldvec() all args";
+my $pdp = zeroes($p);
+rldvec($pf,$pv,$pdp);
+is_pdl $pdp, $p, "rldvec() pre-alloc";
 is_pdl enumvec($p), indx([0,1,2,0,1,0]), "enumvec()";
 is_pdl enumvecg($p), indx([0,0,0,1,1,2]), "enumvecg()";
 
@@ -413,6 +418,16 @@ is_pdl $pv, $pv_expect, "rleND():2d:elts";
 
 $pd = rldND($pf,$pv);
 is_pdl $pd, $p, "rldND():2d";
+my $pfnz = which $pf;
+my $pfr = $pf->dice($pfnz);
+my $pvr = $pv->dice('X', $pfnz);
+my $pdr = rldND($pfr, $pvr);
+is_pdl $pdr, $p, "rldND() nonzero freqs";
+rldND($pfr, $pvr, my $pdn_nd = PDL->null);
+is_pdl $pdn_nd, $p, "rldND() all args";
+my $pdpND = zeroes($p);
+rldND($pfr, $pvr, $pdpND);
+is_pdl $pdpND, $p, "rldND() pre-alloc";
 
 ## rleND, rldND: Nd
 my $pnd1 = (1  *(sequence(long, 2,3  )+1))->slice(",,*3");
@@ -432,6 +447,8 @@ is_pdl $pv_nd, $pv_expect_nd, "rleND():Nd:elts";
 ## 11..11: test rldND(): Nd
 my $pd_nd = rldND($pf_nd,$pv_nd);
 is_pdl $pd_nd, $p_nd, "rldND():Nd";
+rldND($pf_nd,$pv_nd,my $pd_nd_n = PDL->null);
+is_pdl $pd_nd_n, $p_nd, "rldND():Nd all args";
 
 ## 12..12: test enumvec(): nd
 my $v_nd = $p_nd->clump(2);
@@ -453,6 +470,8 @@ my $seqs = zeroes(short, 0);
 $seqs  = $seqs->append(sequence(short,$_)) foreach ($lens->list);
 $seqs += $lens->rld($offs);
 is_pdl $lens->rldseq($offs), $seqs, "rldseq():data";
+$lens->rldseq($offs, my $seq_dec = null);
+is_pdl $seq_dec, $seqs, "rldseq():null";
 my ($len_got,$off_got) = $seqs->rleseq();
 is $off_got->type, $seqs->type, "rleseq():type";
 is_pdl $len_got->where($len_got), $lens->where($lens), "rleseq():lens";