diff --git a/app/Http/Controllers/InvoiceController.php b/app/Http/Controllers/InvoiceController.php
index 0106f6cf8937..b18951594d84 100644
--- a/app/Http/Controllers/InvoiceController.php
+++ b/app/Http/Controllers/InvoiceController.php
@@ -611,4 +611,15 @@ class InvoiceController extends BaseController
 
         return View::make('invoices.history', $data);
     }
+
+    public function checkInvoiceNumber($invoiceNumber)
+    {
+        $count = Invoice::scope()
+                    ->whereInvoiceNumber($invoiceNumber)
+                    ->withTrashed()
+                    ->count();
+
+        return $count ? RESULT_FAILURE : RESULT_SUCCESS;
+    }
+
 }
diff --git a/app/Http/routes.php b/app/Http/routes.php
index e0062cc1f71a..ae10edc82a3f 100644
--- a/app/Http/routes.php
+++ b/app/Http/routes.php
@@ -125,7 +125,8 @@ Route::group(['middleware' => 'auth:user'], function() {
     Route::get('view_archive/{entity_type}/{visible}', 'AccountController@setTrashVisible');
     Route::get('hide_message', 'HomeController@hideMessage');
     Route::get('force_inline_pdf', 'UserController@forcePDFJS');
-    Route::get('account/getSearchData', ['as' => 'getSearchData', 'uses' => 'AccountController@getSearchData']);
+    Route::get('account/get_search_data', ['as' => 'get_search_data', 'uses' => 'AccountController@getSearchData']);
+    Route::get('check_invoice_number/{invoice_number}', 'InvoiceController@checkInvoiceNumber');
 
     Route::get('settings/user_details', 'AccountController@showUserDetails');
     Route::post('settings/user_details', 'AccountController@saveUserDetails');
diff --git a/resources/views/header.blade.php b/resources/views/header.blade.php
index 4eaa4de24a4e..2ca594363631 100644
--- a/resources/views/header.blade.php
+++ b/resources/views/header.blade.php
@@ -234,7 +234,7 @@
 
     if (!window.loadedSearchData) {
         trackEvent('/activity', '/search');
-        var request = $.get('{{ URL::route('getSearchData') }}', function(data) {
+        var request = $.get('{{ URL::route('get_search_data') }}', function(data) {
           $('#search').typeahead({
             hint: true,
             highlight: true,
diff --git a/resources/views/invoices/edit.blade.php b/resources/views/invoices/edit.blade.php
index 3ede53d95cbc..0ee90310192c 100644
--- a/resources/views/invoices/edit.blade.php
+++ b/resources/views/invoices/edit.blade.php
@@ -162,6 +162,8 @@
             <span data-bind="visible: !is_recurring()">
             {!! Former::text('invoice_number')
                         ->label(trans("texts.{$entityType}_number_short"))
+                        ->onchange('checkInvoiceNumber()')
+                        ->addGroupClass('invoice-number')
                         ->data_bind("value: invoice_number, valueUpdate: 'afterkeydown'") !!}
             </span>
             @if($account->getTokenGatewayId())
@@ -1296,6 +1298,11 @@
             return false;
         }
 
+        // check invoice number is unique
+        if ($('.invoice-number').hasClass('has-error')) {
+            return false;
+        }
+
         if (!isSaveValid()) {
             model.showClientForm();
             return false;
diff --git a/resources/views/invoices/knockout.blade.php b/resources/views/invoices/knockout.blade.php
index 49a538c5db27..5ff34c6aaf0f 100644
--- a/resources/views/invoices/knockout.blade.php
+++ b/resources/views/invoices/knockout.blade.php
@@ -895,4 +895,25 @@ ko.bindingHandlers.productTypeahead = {
     }
 };
 
+function checkInvoiceNumber() {
+    var url = '{{ url('check_invoice_number') }}/' + $('#invoice_number').val();
+    $.get(url, function(data) {
+        var isValid = data == '{{ RESULT_SUCCESS }}' ? true : false;
+        if (isValid) {
+            $('.invoice-number')
+                .removeClass('has-error')
+                .find('span')
+                .hide();
+        } else {
+            if ($('.invoice-number').hasClass('has-error')) {
+                return;
+            }
+            $('.invoice-number')
+                .addClass('has-error')
+                .find('div')
+                .append('<span class="help-block">{{ trans('validation.unique', ['attribute' => trans('texts.invoice_number')]) }}</span>');
+        }
+    });
+}
+
 </script>