diff --git a/lib/TableNibbler.pm b/lib/TableNibbler.pm
index f1a0f860..788598ca 100644
--- a/lib/TableNibbler.pm
+++ b/lib/TableNibbler.pm
@@ -82,6 +82,7 @@ sub generate_asc_stmt {
       @asc_cols = $asc_cols[0];
    }
    elsif ( my $n = $args{n_index_cols} ) {
+      $n = scalar @asc_cols if $n > @asc_cols;
       PTDEBUG && _d('Ascending only first', $n, 'columns');
       @asc_cols = @asc_cols[0..($n-1)];
    }
diff --git a/t/lib/TableNibbler.t b/t/lib/TableNibbler.t
index 480704eb..51fe17cf 100644
--- a/t/lib/TableNibbler.t
+++ b/t/lib/TableNibbler.t
@@ -9,7 +9,7 @@ BEGIN {
 use strict;
 use warnings FATAL => 'all';
 use English qw(-no_match_vars);
-use Test::More tests => 25;
+use Test::More tests => 26;
 
 use TableParser;
 use TableNibbler;
@@ -325,6 +325,39 @@ is_deeply(
    'Use only N left-most columns of the index',
 );
 
+is_deeply(
+   $n->generate_asc_stmt(
+      tbl_struct   => $t,
+      cols         => $t->{cols},
+      index        => 'rental_date',
+      n_index_cols => 5,
+   ),
+   {
+      cols  => [qw(rental_id rental_date inventory_id customer_id
+                  return_date staff_id last_update)],
+      index => 'rental_date',
+      where => '((`rental_date` > ?) OR (`rental_date` = ? AND `inventory_id` > ?)'
+         . ' OR (`rental_date` = ? AND `inventory_id` = ? AND `customer_id` >= ?))',
+      slice => [1, 1, 2, 1, 2, 3],
+      scols => [qw(rental_date rental_date inventory_id rental_date inventory_id customer_id)],
+      boundaries => {
+         '>=' => '((`rental_date` > ?) OR (`rental_date` = ? AND '
+            . '`inventory_id` > ?) OR (`rental_date` = ? AND `inventory_id` '
+            . '= ? AND `customer_id` >= ?))',
+         '>' => '((`rental_date` > ?) OR (`rental_date` = ? AND '
+            . '`inventory_id` > ?) OR (`rental_date` = ? AND `inventory_id` '
+            . '= ? AND `customer_id` > ?))',
+         '<=' => '((`rental_date` < ?) OR (`rental_date` = ? AND '
+            . '`inventory_id` < ?) OR (`rental_date` = ? AND `inventory_id` '
+            . '= ? AND `customer_id` <= ?))',
+         '<' => '((`rental_date` < ?) OR (`rental_date` = ? AND '
+            . '`inventory_id` < ?) OR (`rental_date` = ? AND `inventory_id` '
+            . '= ? AND `customer_id` < ?))',
+      },
+   },
+   "Don't crash if N > number of index columns"
+);
+
 is_deeply(
    $n->generate_asc_stmt(
       tbl_struct => $t,
diff --git a/t/pt-table-checksum/chunk_index.t b/t/pt-table-checksum/chunk_index.t
index 14879d7e..969234f4 100644
--- a/t/pt-table-checksum/chunk_index.t
+++ b/t/pt-table-checksum/chunk_index.t
@@ -25,7 +25,7 @@ if ( !$dbh ) {
    plan skip_all => 'Cannot connect to sandbox master';
 }
 else {
-   plan tests => 14;
+   plan tests => 15;
 }
 
 # The sandbox servers run with lock_wait_timeout=3 and it's not dynamic
@@ -199,6 +199,11 @@ ok(
    ),
    "--chunk-index index:n"
 );
+         
+         pt_table_checksum::main(
+            $master_dsn, '--max-load', '',
+            qw(--lock-wait-timeout 3 --chunk-size 5000  -t sakila.rental),
+            qw(--chunk-index rental_date:5 --explain --explain));
 
 # #############################################################################
 # Done.