diff --git a/lib/NGCP/Panel/Utils/Preferences.pm b/lib/NGCP/Panel/Utils/Preferences.pm
index 238509d850..b2550fdfc0 100644
--- a/lib/NGCP/Panel/Utils/Preferences.pm
+++ b/lib/NGCP/Panel/Utils/Preferences.pm
@@ -885,29 +885,20 @@ sub update_preferences {
                     last SWITCH;
                 };
                 /^allowed_clis$/ && do {
-                    if ($replace) {
-                        #check duplicates in case of PUT
-                        if ($resource->{$pref}) {
-                            my %seen;
-                            foreach my $allowed_cli (@{$resource->{$pref}}) {
-                                next unless $seen{$allowed_cli}++;
-                                $c->log->error("Duplicate $pref value: ".$allowed_cli);
-                                &$err_code(HTTP_UNPROCESSABLE_ENTITY, "Duplicate $pref value: ".$allowed_cli);
-                                return;
-                            }
-                        }
-                    }
-                    else {
+                    my $old_seen = {};
+                    unless ($replace) {
                         #in case of PATCH, check duplicates only for new values, since there could already be duplicates in some systems
-                        if ($resource->{$pref} && $old_resource->{$pref}) {
-                            my @new_clis = @{$resource->{$pref}}[scalar @{$old_resource->{$pref}} .. scalar @{$resource->{$pref}} - 1];
-                            my %existing_clis = map {$_ => 1} @{$old_resource->{$pref}};
-                            my ($allowed_cli) = grep { exists $existing_clis{$_} } @new_clis;
-                            if ( $allowed_cli ) {
-                                $c->log->error("Duplicate $pref value: ".$allowed_cli);
-                                &$err_code(HTTP_UNPROCESSABLE_ENTITY, "Duplicate $pref value: ".$allowed_cli);
-                                return;
-                            }
+                        ($old_seen) = array_to_map($old_resource->{$pref},undef,undef,'first');
+                    }   
+                    my $seen = {};
+                    foreach my $allowed_cli (@{$resource->{$pref} // []}) {
+                        next if exists $old_seen->{$allowed_cli};
+                        if (exists $seen->{$allowed_cli}) {
+                            $c->log->error("Duplicate $pref value: ".$allowed_cli);
+                            &$err_code(HTTP_UNPROCESSABLE_ENTITY, "Duplicate $pref value: ".$allowed_cli);
+                            return;
+                        } else {
+                            $seen->{$allowed_cli} = 1;
                         }
                     }
                 };