diff --git a/bin/pt-online-schema-change b/bin/pt-online-schema-change
index d2a0b598..592630e4 100755
--- a/bin/pt-online-schema-change
+++ b/bin/pt-online-schema-change
@@ -5690,7 +5690,7 @@ sub next {
       if ( !$self->{have_rows} ) {
          $self->{nibbleno}++;
          PTDEBUG && _d('Nibble:', $self->{nibble_sth}->{Statement}, 'params:',
-            join(', ', (@{$self->{lower} || []}, @{$self->{upper} || []})));
+            join(', ', (@{$self->{lower}} || [], @{$self->{upper} }||[])));
          if ( my $callback = $self->{callbacks}->{exec_nibble} ) {
             $self->{have_rows} = $callback->(%callback_args);
          }
@@ -6089,7 +6089,7 @@ sub _next_boundaries {
 
 
    PTDEBUG && _d($self->{ub_sth}->{Statement}, 'params:',
-      join(', ', @{$self->{lower}}), $self->{limit});
+      join(', ', @{$self->{lower}} || []), $self->{limit});
    $self->{ub_sth}->execute(@{$self->{lower}}, $self->{limit});
    my $boundary = $self->{ub_sth}->fetchall_arrayref();
    PTDEBUG && _d('Next boundary:', Dumper($boundary));
@@ -6130,6 +6130,9 @@ sub identical_boundaries {
       if scalar @$b1 != scalar @$b2;  # shouldn't happen
    my $n_vals = scalar @$b1;
    for my $i ( 0..($n_vals-1) ) {
+      next if (!defined($b1->[$i]) && !defined($b2->[$i]));
+      return 0 if (!defined($b1->[$i]) && defined($b2->[$i])); # diff
+      return 0 if (defined($b1->[$i]) && !defined($b2->[$i])); # diff
       return 0 if $b1->[$i] ne $b2->[$i]; # diff
    }
    return 1;
diff --git a/t/pt-online-schema-change/pt-1574.t b/t/pt-online-schema-change/pt-1574.t
index 6ea4d96a..343d51d5 100644
--- a/t/pt-online-schema-change/pt-1574.t
+++ b/t/pt-online-schema-change/pt-1574.t
@@ -53,6 +53,9 @@ $sb->load_file('master', "t/pt-online-schema-change/samples/pt-1574.sql");
     stderr => 1,
 );
 
+my $sql_mode = $dbh->selectcol_arrayref('SELECT @@sql_mode');
+warn Data::Dumper::Dumper($sql_mode);
+
 isnt(
     $exit_status,
     0,
diff --git a/t/pt-online-schema-change/samples/pt-1574.sql b/t/pt-online-schema-change/samples/pt-1574.sql
index f0feea2a..2e5fd368 100644
--- a/t/pt-online-schema-change/samples/pt-1574.sql
+++ b/t/pt-online-schema-change/samples/pt-1574.sql
@@ -22,12 +22,13 @@ INSERT INTO `test`.`t1` VALUES
 (NULL,NULL,NULL);
 
 
-CREATE TABLE `test`.`t2` (
-`id` int(11) DEFAULT NULL,
-`site_name` varchar(25) PRIMARY KEY,
-`last_update` datetime DEFAULT NULL,
-UNIQUE KEY `idx_id` (`id`),
-KEY `idx_last_update` (`last_update`)
+CREATE TABLE `t2` (
+  `id` int(11) DEFAULT NULL,
+  `site_name` varchar(25) NOT NULL,
+  `last_update` datetime DEFAULT NULL,
+  PRIMARY KEY (`site_name`),
+  UNIQUE KEY `idx_id` (`id`),
+  KEY `idx_last_update` (`last_update`)
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1;
 
 INSERT INTO `test`.`t2` VALUES