diff --git a/tools/test.pl b/tools/test.pl
index 83bfc913d..388ab0a84 100755
--- a/tools/test.pl
+++ b/tools/test.pl
@@ -330,9 +330,14 @@ sub init_db_word_rand
       }
     }
 
-    # longer than 31 does not work for -a 0 in optimized mode
+    # for non-fixed password length algorithms
 
-    $len_max = ($len_max >= 31) ? 31 : $len_max;
+    if ($len_min != $len_max)
+    {
+      # longer than 31 does not work for -a 0 in optimized mode
+
+      $len_max = ($len_max >= 31) ? 31 : $len_max;
+    }
   }
 
   my $outputs_possible = $len_max - $len_min;
@@ -341,7 +346,7 @@ sub init_db_word_rand
 
   my @pool;
 
-  for my $len ($len_min + 1 .. $len_max - 1)
+  for (my $len = $len_min + 1; $len < $len_max - 1; $len++)
   {
     push @pool, $len;
   }
diff --git a/tools/test_modules/m15400.pm b/tools/test_modules/m15400.pm
new file mode 100644
index 000000000..eb8395170
--- /dev/null
+++ b/tools/test_modules/m15400.pm
@@ -0,0 +1,97 @@
+#!/usr/bin/env perl
+
+##
+## Author......: See docs/credits.txt
+## License.....: MIT
+##
+
+use strict;
+use warnings;
+
+use Crypt::OpenSSH::ChachaPoly;
+
+sub module_constraints { [[-1, -1], [-1, -1], [32, 32], [-1, -1], [-1, -1]] }
+
+sub module_generate_hash
+{
+  my $word   = shift;
+  my $salt   = shift;
+  my $param  = shift;
+  my $param2 = shift;
+  my $param3 = shift;
+
+  my $counter;
+  my $offset;
+  my $iv;
+
+  if (defined $param)
+  {
+    $counter = $param;
+    $offset  = $param2;
+    $iv      = $param3;
+  }
+  else
+  {
+    $counter = "0400000000000003";
+    $offset  = int (rand (63));
+    $iv      = "0200000000000001";
+  }
+
+  my $plaintext = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz0a2b4c6d8e";
+  my $eight_byte_iv = pack ("H*", $iv);
+  my $eight_byte_counter = pack ("H*", $counter);
+  my $pad_len = 32 - length ($word);
+  my $key = $word . "\0" x $pad_len;
+
+  my $cipher = Crypt::OpenSSH::ChachaPoly->new ($key);
+
+  $cipher->ivsetup ($eight_byte_iv, $eight_byte_counter);
+
+  my $enc = $cipher->encrypt ($plaintext);
+
+  my $enc_offset = substr ($enc, $offset, 8);
+
+  my $hash_buf = $enc_offset;
+
+  my $hash = sprintf ("\$chacha20\$\*%s\*%d\*%s\*%s\*%s", $counter, $offset, $iv, unpack ("H*", substr ($plaintext, $offset, 8)), unpack ("H*", $enc_offset));
+
+  return $hash;
+}
+
+sub module_verify_hash
+{
+  my $line = shift;
+
+  my $index1 = index ($line, ':');
+
+  return if ($index1 < 0);
+
+  my $hash_in = substr ($line, 0, $index1);
+
+  my $word = substr ($line, $index1 + 1);
+
+  return if (length ($hash_in) < 11);
+
+  return unless (substr ($hash_in, 0, 11) eq "\$chacha20\$\*");
+
+  my @data = split ('\*', $hash_in);
+
+  return unless (scalar (@data) == 6);
+
+  my $param  = $data[1]; # counter
+  my $param2 = $data[2]; # offset
+  my $param3 = $data[3]; # iv
+
+  return unless defined $param;
+  return unless defined $param2;
+  return unless defined $param3;
+  return unless defined $word;
+
+  $word = pack_if_HEX_notation ($word);
+
+  my $new_hash = module_generate_hash ($word, undef, $param, $param2, $param3);
+
+  return ($new_hash, $word);
+}
+
+1;