diff --git a/bin/pt-online-schema-change b/bin/pt-online-schema-change
index 2690bf36..98112524 100755
--- a/bin/pt-online-schema-change
+++ b/bin/pt-online-schema-change
@@ -5495,7 +5495,7 @@ sub _find_best_index {
       }
       @possible_indexes = sort {
          my $cmp
-            = $indexes->{$b}->{cardinality} <=> $indexes->{$b}->{cardinality};
+            = $indexes->{$b}->{cardinality} <=> $indexes->{$a}->{cardinality};
          if ( $cmp == 0 ) {
             $cmp = scalar @{$indexes->{$b}->{cols}}
                <=> scalar @{$indexes->{$a}->{cols}};
diff --git a/bin/pt-table-checksum b/bin/pt-table-checksum
index 34e8b9a3..bc3387a6 100755
--- a/bin/pt-table-checksum
+++ b/bin/pt-table-checksum
@@ -6479,7 +6479,7 @@ sub _find_best_index {
       }
       @possible_indexes = sort {
          my $cmp
-            = $indexes->{$b}->{cardinality} <=> $indexes->{$b}->{cardinality};
+            = $indexes->{$b}->{cardinality} <=> $indexes->{$a}->{cardinality};
          if ( $cmp == 0 ) {
             $cmp = scalar @{$indexes->{$b}->{cols}}
                <=> scalar @{$indexes->{$a}->{cols}};