diff --git a/bin/pt-archiver b/bin/pt-archiver
index 9e6951bf..47b2f7b4 100755
--- a/bin/pt-archiver
+++ b/bin/pt-archiver
@@ -3220,7 +3220,7 @@ sub generate_cmp_where {
             push @clause, "($val IS NULL OR $quo $type $val)";
          }
          elsif ( $type =~ m/>/ ) {
-            push @clause, "(($val IS NULL AND $quo IS NOT NULL) OR ($quo $cmp $val)";
+            push @clause, "($val IS NULL AND $quo IS NOT NULL) OR ($quo $cmp $val)";
          }
          else { # If $type =~ m/</ ) {
             push @clauses, "(($val IS NOT NULL AND $quo IS NULL) OR ($quo $cmp $val))";
@@ -3234,7 +3234,7 @@ sub generate_cmp_where {
          push @clause, ($type =~ m/=/ && $end ? "$quo $type $val" : "$quo $cmp $val");
       }
 
-      push @clauses, '(' . join(' AND ', @clause) . ')';
+      push @clauses, '(' . join(' AND ', @clause) . ')' if @clause;
    }
    my $result = '(' . join(' OR ', @clauses) . ')';
    my $where = {
diff --git a/bin/pt-online-schema-change b/bin/pt-online-schema-change
index 45973618..63a44a47 100755
--- a/bin/pt-online-schema-change
+++ b/bin/pt-online-schema-change
@@ -2999,7 +2999,7 @@ sub generate_asc_stmt {
 
    die "Index '$index' does not exist in table"
       unless exists $tbl_struct->{keys}->{$index};
-   PTDEBUG && _d('Will ascend index', $index);
+   PTDEBUG && _d('Will ascend index', $index);  
 
    my @asc_cols = @{$tbl_struct->{keys}->{$index}->{cols}};
    if ( $args{asc_first} ) {
@@ -3102,7 +3102,7 @@ sub generate_cmp_where {
             push @clause, "($val IS NULL OR $quo $type $val)";
          }
          elsif ( $type =~ m/>/ ) {
-            push @clause, "(($val IS NULL AND $quo IS NOT NULL) OR ($quo $cmp $val)";
+            push @clause, "($val IS NULL AND $quo IS NOT NULL) OR ($quo $cmp $val)";
          }
          else { # If $type =~ m/</ ) {
             push @clauses, "(($val IS NOT NULL AND $quo IS NULL) OR ($quo $cmp $val))";
@@ -3116,7 +3116,7 @@ sub generate_cmp_where {
          push @clause, ($type =~ m/=/ && $end ? "$quo $type $val" : "$quo $cmp $val");
       }
 
-      push @clauses, '(' . join(' AND ', @clause) . ')';
+      push @clauses, '(' . join(' AND ', @clause) . ')' if @clause;
    }
    my $result = '(' . join(' OR ', @clauses) . ')';
    my $where = {
diff --git a/bin/pt-table-checksum b/bin/pt-table-checksum
index e375da22..72cd754e 100755
--- a/bin/pt-table-checksum
+++ b/bin/pt-table-checksum
@@ -4872,7 +4872,7 @@ sub generate_asc_stmt {
 
    die "Index '$index' does not exist in table"
       unless exists $tbl_struct->{keys}->{$index};
-   PTDEBUG && _d('Will ascend index', $index);
+   PTDEBUG && _d('Will ascend index', $index);  
 
    my @asc_cols = @{$tbl_struct->{keys}->{$index}->{cols}};
    if ( $args{asc_first} ) {
@@ -4975,7 +4975,7 @@ sub generate_cmp_where {
             push @clause, "($val IS NULL OR $quo $type $val)";
          }
          elsif ( $type =~ m/>/ ) {
-            push @clause, "(($val IS NULL AND $quo IS NOT NULL) OR ($quo $cmp $val)";
+            push @clause, "($val IS NULL AND $quo IS NOT NULL) OR ($quo $cmp $val)";
          }
          else { # If $type =~ m/</ ) {
             push @clauses, "(($val IS NOT NULL AND $quo IS NULL) OR ($quo $cmp $val))";
@@ -4989,7 +4989,7 @@ sub generate_cmp_where {
          push @clause, ($type =~ m/=/ && $end ? "$quo $type $val" : "$quo $cmp $val");
       }
 
-      push @clauses, '(' . join(' AND ', @clause) . ')';
+      push @clauses, '(' . join(' AND ', @clause) . ')' if @clause;
    }
    my $result = '(' . join(' OR ', @clauses) . ')';
    my $where = {
diff --git a/bin/pt-table-sync b/bin/pt-table-sync
index 72467551..6384afad 100755
--- a/bin/pt-table-sync
+++ b/bin/pt-table-sync
@@ -6505,7 +6505,7 @@ sub generate_cmp_where {
             push @clause, "($val IS NULL OR $quo $type $val)";
          }
          elsif ( $type =~ m/>/ ) {
-            push @clause, "(($val IS NULL AND $quo IS NOT NULL) OR ($quo $cmp $val)";
+            push @clause, "($val IS NULL AND $quo IS NOT NULL) OR ($quo $cmp $val)";
          }
          else { # If $type =~ m/</ ) {
             push @clauses, "(($val IS NOT NULL AND $quo IS NULL) OR ($quo $cmp $val))";
@@ -6519,7 +6519,7 @@ sub generate_cmp_where {
          push @clause, ($type =~ m/=/ && $end ? "$quo $type $val" : "$quo $cmp $val");
       }
 
-      push @clauses, '(' . join(' AND ', @clause) . ')';
+      push @clauses, '(' . join(' AND ', @clause) . ')' if @clause;
    }
    my $result = '(' . join(' OR ', @clauses) . ')';
    my $where = {
diff --git a/lib/TableNibbler.pm b/lib/TableNibbler.pm
index 122e4e7b..fd7befd2 100644
--- a/lib/TableNibbler.pm
+++ b/lib/TableNibbler.pm
@@ -197,7 +197,7 @@ sub generate_cmp_where {
             push @clause, "($val IS NULL OR $quo $type $val)";
          }
          elsif ( $type =~ m/>/ ) {
-            push @clause, "(($val IS NULL AND $quo IS NOT NULL) OR ($quo $cmp $val)";
+            push @clause, "($val IS NULL AND $quo IS NOT NULL) OR ($quo $cmp $val)";
          }
          else { # If $type =~ m/</ ) {
             push @clauses, "(($val IS NOT NULL AND $quo IS NULL) OR ($quo $cmp $val))";
@@ -212,7 +212,7 @@ sub generate_cmp_where {
       }
 
       # Add the clause to the larger WHERE clause.
-      push @clauses, '(' . join(' AND ', @clause) . ')';
+      push @clauses, '(' . join(' AND ', @clause) . ')' if @clause;
    }
    my $result = '(' . join(' OR ', @clauses) . ')';
    my $where = {
diff --git a/t/pt-table-checksum/samples/oversize-chunks.txt b/t/pt-table-checksum/samples/oversize-chunks.txt
index f4a86493..0bf8a9f6 100644
--- a/t/pt-table-checksum/samples/oversize-chunks.txt
+++ b/t/pt-table-checksum/samples/oversize-chunks.txt
@@ -6,9 +6,9 @@ Starting checksum ...
 
 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('#', convert(`c` using utf8mb4), CONCAT(ISNULL(`c`)))) AS UNSIGNED)), 10, 16)), 0) AS crc FROM `osc`.`t2` FORCE INDEX(`c`) WHERE (((? IS NULL OR `c` >= ?))) AND (((? IS NULL OR `c` <= ?))) /*checksum chunk*/
 
-REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `osc`.`t2` FORCE INDEX(`c`) WHERE ((((? IS NOT NULL AND `c` IS NULL) OR (`c` < ?)))) ORDER BY `c` /*past lower chunk*/
+REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `osc`.`t2` FORCE INDEX(`c`) WHERE (((? IS NOT NULL AND `c` IS NULL) OR (`c` < ?))) ORDER BY `c` /*past lower chunk*/
 
-REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `osc`.`t2` FORCE INDEX(`c`) WHERE ((((? IS NULL AND `c` IS NOT NULL) OR (`c` > ?)))) ORDER BY `c` /*past upper chunk*/
+REPLACE INTO `percona`.`checksums` (db, tbl, chunk, chunk_index, lower_boundary, upper_boundary, this_cnt, this_crc) SELECT ?, ?, ?, ?, ?, ?, COUNT(*), '0' FROM `osc`.`t2` FORCE INDEX(`c`) WHERE (((? IS NULL AND `c` IS NOT NULL) OR (`c` > ?))) ORDER BY `c` /*past upper chunk*/
 
 SELECT /*!40001 SQL_NO_CACHE */ `c`, `c` FROM `osc`.`t2` FORCE INDEX(`c`) WHERE (((? IS NULL OR `c` >= ?))) ORDER BY `c` LIMIT ?, 2 /*next chunk boundary*/