diff --git a/Kernel/Modules/AgentTicketCompose.pm b/Kernel/Modules/AgentTicketCompose.pm
index 84a0a92eb4b..214f451c686 100644
--- a/Kernel/Modules/AgentTicketCompose.pm
+++ b/Kernel/Modules/AgentTicketCompose.pm
@@ -1295,6 +1295,36 @@ sub Run {
             NoCache     => 1,
         );
     }
+    elsif ( $Self->{Subaction} eq 'CheckSubject' ) {
+
+        # Inform a user that article subject will be empty if contains only the ticket hook (if nothing is modified).
+        my $Message = $LayoutObject->{LanguageObject}->Translate(
+            'Article subject will be empty if the subject contains only the ticket hook!'
+        );
+
+        my $Subject = $ParamObject->GetParam( Param => 'Subject' );
+
+        my $CleanedSubject = $TicketObject->TicketSubjectClean(
+            TicketNumber => $Ticket{TicketNumber},
+            Subject      => $Subject,
+        );
+
+        my $Empty = !length $CleanedSubject;
+
+        my $JSON = $LayoutObject->JSONEncode(
+            Data => {
+                Empty   => $Empty ? 1 : 0,
+                Message => $Message,
+            }
+        );
+
+        return $LayoutObject->Attachment(
+            ContentType => 'application/json; charset=' . $LayoutObject->{Charset},
+            Content     => $JSON,
+            Type        => 'inline',
+            NoCache     => 1,
+        );
+    }
     else {
         my $Output = $LayoutObject->Header(
             Value     => $Ticket{TicketNumber},
@@ -1302,13 +1332,6 @@ sub Run {
             BodyClass => 'Popup',
         );
 
-        # Inform a user that article subject will be empty if contains only the ticket hook (if nothing is modified).
-        $Output .= $LayoutObject->Notify(
-            Data => $LayoutObject->{LanguageObject}->Translate(
-                'Article subject will be empty if the subject contains only the ticket hook!'
-            ),
-        );
-
         # get std attachment object
         my $StdAttachmentObject = $Kernel::OM->Get('Kernel::System::StdAttachment');
 
diff --git a/var/httpd/htdocs/js/Core.Agent.TicketCompose.js b/var/httpd/htdocs/js/Core.Agent.TicketCompose.js
index 49d1e8d8c38..0eca54a94cc 100644
--- a/var/httpd/htdocs/js/Core.Agent.TicketCompose.js
+++ b/var/httpd/htdocs/js/Core.Agent.TicketCompose.js
@@ -44,6 +44,10 @@ Core.Agent.TicketCompose = (function (TargetNS) {
             Core.AJAX.FormUpdate($('#ComposeTicket'), 'AJAXUpdate', 'StateID', Core.Config.Get('DynamicFieldNames'));
         });
 
+        // check subject
+        CheckSubject();
+        $('#Subject').on('change', CheckSubject);
+
         // add 'To' customer users
         if (typeof EmailAddressesTo !== 'undefined') {
             EmailAddressesTo.forEach(function(ToCustomer) {
@@ -68,6 +72,27 @@ Core.Agent.TicketCompose = (function (TargetNS) {
         }
     };
 
+    function CheckSubject () {
+        var CurrentSubject = $('#Subject').val();
+        $('#SubjectWarning').remove();
+
+        $.ajax({
+            url: Core.Config.Get('Baselink'),
+            type: 'POST',
+            data: {
+                Action: Core.Config.Get('Action'),
+                Subaction: 'CheckSubject',
+                Subject: CurrentSubject,
+                TicketID: $('input[name=TicketID]').val(),
+            },
+            success : function(Response) {
+                if (Response.Empty) {
+                    $('#AppWrapper').prepend('<div class="MessageBox Notice" id="SubjectWarning"><p>' + Response.Message + '</div>');
+                }
+            }
+        });
+    }
+
     Core.Init.RegisterNamespace(TargetNS, 'APP_MODULE');
 
     return TargetNS;