diff --git a/bin/pt-online-schema-change b/bin/pt-online-schema-change
index c1cdcabd..c5ab5b15 100755
--- a/bin/pt-online-schema-change
+++ b/bin/pt-online-schema-change
@@ -5132,12 +5132,12 @@ sub main {
    # https://bugs.launchpad.net/percona-toolkit/+bug/1010232
    my ($chunk_index, $n_chunk_index_cols)
       = split(':', $o->get('chunk-index') || '');
-   if ( defined $chunk_index && !$chunk_index ) {
+   if ( defined $chunk_index && $chunk_index eq '' ) {
       $o->save_error('--chunk-index cannot be an empty string');
    }
    if ( defined $n_chunk_index_cols
         && (!$n_chunk_index_cols
-            || $n_chunk_index_cols =~ m/[^\d]/
+            || $n_chunk_index_cols =~ m/\D/
             || $n_chunk_index_cols < 1) ) {
       $o->save_error('Invalid number of --chunk-index columns: '
          . $n_chunk_index_cols);
diff --git a/bin/pt-table-checksum b/bin/pt-table-checksum
index 12b4b8a1..fe47c042 100755
--- a/bin/pt-table-checksum
+++ b/bin/pt-table-checksum
@@ -6093,12 +6093,12 @@ sub main {
    # https://bugs.launchpad.net/percona-toolkit/+bug/1010232
    my ($chunk_index, $n_chunk_index_cols)
       = split(':', $o->get('chunk-index') || '');
-   if ( defined $chunk_index && !$chunk_index ) {
+   if ( defined $chunk_index && $chunk_index eq '' ) {
       $o->save_error('--chunk-index cannot be an empty string');
    }
    if ( defined $n_chunk_index_cols
         && (!$n_chunk_index_cols
-            || $n_chunk_index_cols =~ m/[^\d]/
+            || $n_chunk_index_cols =~ m/\D/
             || $n_chunk_index_cols < 1) ) {
       $o->save_error('Invalid number of --chunk-index columns: '
          . $n_chunk_index_cols);