diff --git a/bin/pt-table-checksum b/bin/pt-table-checksum
index 48390f7b..03d086a3 100755
--- a/bin/pt-table-checksum
+++ b/bin/pt-table-checksum
@@ -3514,7 +3514,7 @@ sub new {
          . ($args{select} ? $args{select}
                           : join(', ', map { $q->quote($_) } @cols))
          . " FROM " . $q->quote(@{$tbl}{qw(db tbl)})
-         . ($where ? " AND ($where)" : '')
+         . ($where ? " WHERE $where" : '')
          . " /*checksum table*/";
       MKDEBUG && _d('One nibble statement:', $nibble_sql);
 
@@ -3523,7 +3523,7 @@ sub new {
          . ($args{select} ? $args{select}
                           : join(', ', map { $q->quote($_) } @cols))
          . " FROM " . $q->quote(@{$tbl}{qw(db tbl)})
-         . ($where ? " AND ($where)" : '')
+         . ($where ? " WHERE $where" : '')
          . " /*explain checksum table*/";
       MKDEBUG && _d('Explain one nibble statement:', $explain_nibble_sql);
 
diff --git a/lib/NibbleIterator.pm b/lib/NibbleIterator.pm
index 88d4d6a2..91ab19a6 100644
--- a/lib/NibbleIterator.pm
+++ b/lib/NibbleIterator.pm
@@ -95,7 +95,7 @@ sub new {
          . ($args{select} ? $args{select}
                           : join(', ', map { $q->quote($_) } @cols))
          . " FROM " . $q->quote(@{$tbl}{qw(db tbl)})
-         . ($where ? " AND ($where)" : '')
+         . ($where ? " WHERE $where" : '')
          . " /*checksum table*/";
       MKDEBUG && _d('One nibble statement:', $nibble_sql);
 
@@ -104,7 +104,7 @@ sub new {
          . ($args{select} ? $args{select}
                           : join(', ', map { $q->quote($_) } @cols))
          . " FROM " . $q->quote(@{$tbl}{qw(db tbl)})
-         . ($where ? " AND ($where)" : '')
+         . ($where ? " WHERE $where" : '')
          . " /*explain checksum table*/";
       MKDEBUG && _d('Explain one nibble statement:', $explain_nibble_sql);
 
diff --git a/t/lib/NibbleIterator.t b/t/lib/NibbleIterator.t
index 93b61102..5ab973c6 100644
--- a/t/lib/NibbleIterator.t
+++ b/t/lib/NibbleIterator.t
@@ -39,7 +39,7 @@ if ( !$dbh ) {
    plan skip_all => 'Cannot connect to sandbox master';
 }
 else {
-   plan tests => 45;
+   plan tests => 46;
 }
 
 my $q   = new Quoter();
@@ -711,6 +711,21 @@ is_deeply(
    "Nibbles only values in --where clause range"
 );
 
+$ni = make_nibble_iter(
+   sql_file   => "a-z.sql",
+   db         => 'test',
+   tbl        => 't',
+   one_nibble => 1,
+   argv       => [qw(--databases test --where c>'m')],
+);
+1 while $ni->next();
+my $sql = $ni->statements()->{nibble}->{Statement};
+is(
+   $sql,
+   "SELECT `c` FROM `test`.`t` WHERE c>'m' /*checksum table*/",
+   "One nibble SQL with where"
+);
+
 # The real number of rows is 13, but MySQL may estimate a little.
 cmp_ok(
    $ni->row_estimate(),
@@ -719,7 +734,6 @@ cmp_ok(
    "row_estimate()"
 );
 
-
 # ############################################################################
 # Empty table.
 # ############################################################################
diff --git a/t/pt-table-checksum/chunk_index.t b/t/pt-table-checksum/chunk_index.t
index 1d908775..34ff46f4 100644
--- a/t/pt-table-checksum/chunk_index.t
+++ b/t/pt-table-checksum/chunk_index.t
@@ -32,7 +32,7 @@ else {
 # so we need to specify --lock-wait-timeout=3 else the tool will die.
 # And --max-load "" prevents waiting for status variables.
 my $master_dsn = 'h=127.1,P=12345,u=msandbox,p=msandbox';
-my @args       = ($master_dsn, qw(--lock-wait-timeout 3 -d issue_519 --explain --explain --chunk-size 3), '--max-load', '');
+my @args       = ($master_dsn, qw(--lock-wait-timeout 3 --explain --chunk-size 3), '--max-load', '');
 my $output;
 my $out        = "t/pt-table-checksum/samples/";
 
@@ -40,7 +40,7 @@ $sb->load_file('master', "t/pt-table-checksum/samples/issue_519.sql");
 
 ok(
    no_diff(
-      sub { pt_table_checksum::main(@args) },
+      sub { pt_table_checksum::main(@args, qw(-t issue_519.t --explain)) },
       "$out/chunkidx001.txt",
    ),
    "Chooses chunk index by default"
@@ -48,7 +48,8 @@ ok(
 
 ok(
    no_diff(
-      sub { pt_table_checksum::main(@args, qw(--chunk-index dog)) },
+      sub { pt_table_checksum::main(@args, qw(--chunk-index dog),
+         qw(-t issue_519.t --explain)) },
       "$out/chunkidx001.txt",
    ),
    "Chooses chunk index if --chunk-index doesn't exist"
@@ -56,7 +57,8 @@ ok(
 
 ok(
    no_diff(
-      sub { pt_table_checksum::main(@args, qw(--chunk-index myidx)) },
+      sub { pt_table_checksum::main(@args, qw(--chunk-index myidx),
+         qw(-t issue_519.t --explain)) },
       "$out/chunkidx002.txt",
    ),
    "Use --chunk-index"
@@ -66,7 +68,8 @@ ok(
 # is a single column index, so there's really not "left-most".
 ok(
    no_diff(
-      sub { pt_table_checksum::main(@args, qw(--chunk-index y)) },
+      sub { pt_table_checksum::main(@args, qw(--chunk-index y),
+         qw(-t issue_519.t --explain)) },
       "$out/chunkidx003.txt",
    ),
    "Chunks on left-most --chunk-index column"
@@ -79,22 +82,23 @@ ok(
 
 # This issue affect --chunk-index.  Tool should auto-choose chunk-index
 # when --where is given but no explicit --chunk-index|column is given.
-# Given the --where clause, MySQL will prefer the y index.
+# Given the --where clause, MySQL will prefer the idx_fk_country_id index.
 
 ok(
    no_diff(
-      sub { pt_table_checksum::main(@args, "--where", "y > 2009") },
+      sub { pt_table_checksum::main(@args, "--where", "country_id > 100",
+         qw(-t sakila.city)) },
       "$out/chunkidx004.txt",
    ),
    "Auto-chosen --chunk-index for --where (issue 378)"
 );
 
 # If user specifies --chunk-index, then ignore the index MySQL wants to
-# use (y in this case) and use the user's index.
+# use (idx_fk_country_id in this case) and use the user's index.
 ok(
    no_diff(
       sub { pt_table_checksum::main(@args, qw(--chunk-index PRIMARY),
-         "--where", "y > 2009") },
+         "--where", "country_id > 100", qw(-t sakila.city)) },
       "$out/chunkidx005.txt",
    ),
    "Explicit --chunk-index overrides MySQL's index for --where"
diff --git a/t/pt-table-checksum/samples/chunkidx001.txt b/t/pt-table-checksum/samples/chunkidx001.txt
index dcc96f95..62ca8d11 100644
--- a/t/pt-table-checksum/samples/chunkidx001.txt
+++ b/t/pt-table-checksum/samples/chunkidx001.txt
@@ -2,7 +2,7 @@
 -- issue_519.t
 --
 
-REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*) AS cnt, COALESCE(LOWER(CONV(BIT_XOR(CAST(CRC32(CONCAT_WS('#', `i`, `y`, `t`, CONCAT(ISNULL(`t`)))) AS UNSIGNED)), 10, 16)), 0) AS crc FROM `issue_519`.`t` FORCE INDEX(`PRIMARY`) WHERE ((`i` >= ?)) AND ((`i` <= ?)) ORDER BY `i` /*checksum chunk*/
+REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*) AS cnt, COALESCE(LOWER(CONV(BIT_XOR(CAST(CRC32(CONCAT_WS('#', `i`, `y`, `t`, CONCAT(ISNULL(`t`)))) AS UNSIGNED)), 10, 16)), 0) AS crc FROM `issue_519`.`t` FORCE INDEX(`PRIMARY`) WHERE ((`i` >= ?)) AND ((`i` <= ?)) /*checksum chunk*/
 
 REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `issue_519`.`t` FORCE INDEX(`PRIMARY`) WHERE ((`i` < ?)) ORDER BY `i` /*past lower chunk*/
 
diff --git a/t/pt-table-checksum/samples/chunkidx002.txt b/t/pt-table-checksum/samples/chunkidx002.txt
index 5adba728..5b532454 100644
--- a/t/pt-table-checksum/samples/chunkidx002.txt
+++ b/t/pt-table-checksum/samples/chunkidx002.txt
@@ -2,7 +2,7 @@
 -- issue_519.t
 --
 
-REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*) AS cnt, COALESCE(LOWER(CONV(BIT_XOR(CAST(CRC32(CONCAT_WS('#', `i`, `y`, `t`, CONCAT(ISNULL(`t`)))) AS UNSIGNED)), 10, 16)), 0) AS crc FROM `issue_519`.`t` FORCE INDEX(`myidx`) WHERE ((`i` > ?) OR (`i` = ? AND `y` >= ?)) AND ((`i` < ?) OR (`i` = ? AND `y` <= ?)) ORDER BY `i`, `y` /*checksum chunk*/
+REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*) AS cnt, COALESCE(LOWER(CONV(BIT_XOR(CAST(CRC32(CONCAT_WS('#', `i`, `y`, `t`, CONCAT(ISNULL(`t`)))) AS UNSIGNED)), 10, 16)), 0) AS crc FROM `issue_519`.`t` FORCE INDEX(`myidx`) WHERE ((`i` > ?) OR (`i` = ? AND `y` >= ?)) AND ((`i` < ?) OR (`i` = ? AND `y` <= ?)) /*checksum chunk*/
 
 REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `issue_519`.`t` FORCE INDEX(`myidx`) WHERE ((`i` < ?) OR (`i` = ? AND `y` < ?)) ORDER BY `i`, `y` /*past lower chunk*/
 
diff --git a/t/pt-table-checksum/samples/chunkidx003.txt b/t/pt-table-checksum/samples/chunkidx003.txt
index dbdb9090..ba0c7647 100644
--- a/t/pt-table-checksum/samples/chunkidx003.txt
+++ b/t/pt-table-checksum/samples/chunkidx003.txt
@@ -2,7 +2,7 @@
 -- issue_519.t
 --
 
-REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*) AS cnt, COALESCE(LOWER(CONV(BIT_XOR(CAST(CRC32(CONCAT_WS('#', `i`, `y`, `t`, CONCAT(ISNULL(`t`)))) AS UNSIGNED)), 10, 16)), 0) AS crc FROM `issue_519`.`t` FORCE INDEX(`y`) WHERE ((`y` >= ?)) AND ((`y` <= ?)) ORDER BY `y` /*checksum chunk*/
+REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*) AS cnt, COALESCE(LOWER(CONV(BIT_XOR(CAST(CRC32(CONCAT_WS('#', `i`, `y`, `t`, CONCAT(ISNULL(`t`)))) AS UNSIGNED)), 10, 16)), 0) AS crc FROM `issue_519`.`t` FORCE INDEX(`y`) WHERE ((`y` >= ?)) AND ((`y` <= ?)) /*checksum chunk*/
 
 REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `issue_519`.`t` FORCE INDEX(`y`) WHERE ((`y` < ?)) ORDER BY `y` /*past lower chunk*/
 
diff --git a/t/pt-table-checksum/samples/chunkidx004.txt b/t/pt-table-checksum/samples/chunkidx004.txt
index 0a00b1eb..b3ceb684 100644
--- a/t/pt-table-checksum/samples/chunkidx004.txt
+++ b/t/pt-table-checksum/samples/chunkidx004.txt
@@ -1,16 +1,12 @@
 --
--- issue_519.t
+-- sakila.city
 --
 
-REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*) AS cnt, COALESCE(LOWER(CONV(BIT_XOR(CAST(CRC32(CONCAT_WS('#', `i`, `y`, `t`, CONCAT(ISNULL(`t`)))) AS UNSIGNED)), 10, 16)), 0) AS crc FROM `issue_519`.`t` FORCE INDEX(`y`) WHERE ((`y` >= ?)) AND ((`y` <= ?)) AND (y > 2009) ORDER BY `y` /*checksum chunk*/
+REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*) AS cnt, COALESCE(LOWER(CONV(BIT_XOR(CAST(CRC32(CONCAT_WS('#', `city_id`, `city`, `country_id`, `last_update` + 0)) AS UNSIGNED)), 10, 16)), 0) AS crc FROM `sakila`.`city` FORCE INDEX(`idx_fk_country_id`) WHERE ((`country_id` >= ?)) AND ((`country_id` <= ?)) AND (country_id > 100) /*checksum chunk*/
 
-REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `issue_519`.`t` FORCE INDEX(`y`) WHERE ((`y` < ?)) AND (y > 2009) ORDER BY `y` /*past lower chunk*/
+REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `sakila`.`city` FORCE INDEX(`idx_fk_country_id`) WHERE ((`country_id` < ?)) AND (country_id > 100) ORDER BY `country_id` /*past lower chunk*/
 
-REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `issue_519`.`t` FORCE INDEX(`y`) WHERE ((`y` > ?)) AND (y > 2009) ORDER BY `y` /*past upper chunk*/
+REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `sakila`.`city` FORCE INDEX(`idx_fk_country_id`) WHERE ((`country_id` > ?)) AND (country_id > 100) ORDER BY `country_id` /*past upper chunk*/
 
-SELECT /*!40001 SQL_NO_CACHE */ `y` FROM `issue_519`.`t` FORCE INDEX(`y`) WHERE ((`y` >= ?)) AND (y > 2009) ORDER BY `y` LIMIT ?, 2 /*next chunk boundary*/
-
-1 2010 2010
-2  2010
-3 2010 
+SELECT /*!40001 SQL_NO_CACHE */ `country_id` FROM `sakila`.`city` FORCE INDEX(`idx_fk_country_id`) WHERE ((`country_id` >= ?)) AND (country_id > 100) ORDER BY `country_id` LIMIT ?, 2 /*next chunk boundary*/
 
diff --git a/t/pt-table-checksum/samples/chunkidx005.txt b/t/pt-table-checksum/samples/chunkidx005.txt
index b34f386c..ae55d193 100644
--- a/t/pt-table-checksum/samples/chunkidx005.txt
+++ b/t/pt-table-checksum/samples/chunkidx005.txt
@@ -1,16 +1,12 @@
 --
--- issue_519.t
+-- sakila.city
 --
 
-REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*) AS cnt, COALESCE(LOWER(CONV(BIT_XOR(CAST(CRC32(CONCAT_WS('#', `i`, `y`, `t`, CONCAT(ISNULL(`t`)))) AS UNSIGNED)), 10, 16)), 0) AS crc FROM `issue_519`.`t` FORCE INDEX(`PRIMARY`) WHERE ((`i` >= ?)) AND ((`i` <= ?)) AND (y > 2009) ORDER BY `i` /*checksum chunk*/
+REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*) AS cnt, COALESCE(LOWER(CONV(BIT_XOR(CAST(CRC32(CONCAT_WS('#', `city_id`, `city`, `country_id`, `last_update` + 0)) AS UNSIGNED)), 10, 16)), 0) AS crc FROM `sakila`.`city` FORCE INDEX(`PRIMARY`) WHERE ((`city_id` >= ?)) AND ((`city_id` <= ?)) AND (country_id > 100) /*checksum chunk*/
 
-REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `issue_519`.`t` FORCE INDEX(`PRIMARY`) WHERE ((`i` < ?)) AND (y > 2009) ORDER BY `i` /*past lower chunk*/
+REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `sakila`.`city` FORCE INDEX(`PRIMARY`) WHERE ((`city_id` < ?)) AND (country_id > 100) ORDER BY `city_id` /*past lower chunk*/
 
-REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `issue_519`.`t` FORCE INDEX(`PRIMARY`) WHERE ((`i` > ?)) AND (y > 2009) ORDER BY `i` /*past upper chunk*/
+REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `sakila`.`city` FORCE INDEX(`PRIMARY`) WHERE ((`city_id` > ?)) AND (country_id > 100) ORDER BY `city_id` /*past upper chunk*/
 
-SELECT /*!40001 SQL_NO_CACHE */ `i` FROM `issue_519`.`t` FORCE INDEX(`PRIMARY`) WHERE ((`i` >= ?)) AND (y > 2009) ORDER BY `i` LIMIT ?, 2 /*next chunk boundary*/
-
-1 11 11
-2  11
-3 11 
+SELECT /*!40001 SQL_NO_CACHE */ `city_id` FROM `sakila`.`city` FORCE INDEX(`PRIMARY`) WHERE ((`city_id` >= ?)) AND (country_id > 100) ORDER BY `city_id` LIMIT ?, 2 /*next chunk boundary*/