diff --git a/lib/NGCP/Panel/Controller/Customer.pm b/lib/NGCP/Panel/Controller/Customer.pm
index 0c30879b7c..5f28b9c5df 100644
--- a/lib/NGCP/Panel/Controller/Customer.pm
+++ b/lib/NGCP/Panel/Controller/Customer.pm
@@ -653,7 +653,7 @@ sub subscriber_create :Chained('base') :PathPart('subscriber/create') :Args(0) {
                     my $base_number = $pilot->primary_number;
                     if($base_number) {
                         $preferences->{cloud_pbx_base_cli} = $base_number->cc . $base_number->ac . $base_number->sn;
-                        if($form->params->{pbx_extension}) {
+                        if(defined $form->params->{pbx_extension}) {
                             $form->params->{e164}{cc} = $base_number->cc;
                             $form->params->{e164}{ac} = $base_number->ac;
                             $form->params->{e164}{sn} = $base_number->sn . $form->params->{pbx_extension};
@@ -968,7 +968,7 @@ sub pbx_group_create :Chained('base') :PathPart('pbx/group/create') :Args(0) {
                 my $base_number = $pilot->primary_number;
                 if($base_number) {
                     $preferences->{cloud_pbx_base_cli} = $base_number->cc . $base_number->ac . $base_number->sn;
-                    if($form->params->{pbx_extension}) {
+                    if(defined $form->params->{pbx_extension}) {
                         $form->params->{e164}{cc} = $base_number->cc;
                         $form->params->{e164}{ac} = $base_number->ac;
                         $form->params->{e164}{sn} = $base_number->sn . $form->params->{pbx_extension};
diff --git a/lib/NGCP/Panel/Controller/Subscriber.pm b/lib/NGCP/Panel/Controller/Subscriber.pm
index 13f0982c82..748b2bc43c 100644
--- a/lib/NGCP/Panel/Controller/Subscriber.pm
+++ b/lib/NGCP/Panel/Controller/Subscriber.pm
@@ -2281,7 +2281,7 @@ sub edit_master :Chained('master') :PathPart('edit') :Args(0) :Does(ACL) :ACLDet
                         $display_pref->create({ value => $form->params->{display_name} });
                     }
                 }
-                if($form->params->{pbx_extension}) {
+                if(defined $form->params->{pbx_extension}) {
                     my $pref = NGCP::Panel::Utils::Preferences::get_usr_preference_rs(
                             c => $c, attribute => 'cloud_pbx_ext', 
                             prov_subscriber => $prov_subscriber);
diff --git a/lib/NGCP/Panel/Role/API/Subscribers.pm b/lib/NGCP/Panel/Role/API/Subscribers.pm
index 523fd7ff84..e58866d954 100644
--- a/lib/NGCP/Panel/Role/API/Subscribers.pm
+++ b/lib/NGCP/Panel/Role/API/Subscribers.pm
@@ -326,7 +326,7 @@ sub prepare_resource {
         });
 
         if($pilot && $pilot->id != $subscriber_id) {
-            unless($resource->{pbx_extension}) {
+            unless(defined $resource->{pbx_extension}) {
                 $self->error($c, HTTP_UNPROCESSABLE_ENTITY, "A pbx_extension is required if customer is PBX and pilot subscriber exists.");
                 return;
             }