diff --git a/app/Http/ValidationRules/Recurring/UniqueRecurringInvoiceNumberRule.php b/app/Http/ValidationRules/Recurring/UniqueRecurringInvoiceNumberRule.php
new file mode 100644
index 000000000000..2103424b6e14
--- /dev/null
+++ b/app/Http/ValidationRules/Recurring/UniqueRecurringInvoiceNumberRule.php
@@ -0,0 +1,73 @@
+<?php
+/**
+ * Invoice Ninja (https://invoiceninja.com).
+ *
+ * @link https://github.com/invoiceninja/invoiceninja source repository
+ *
+ * @copyright Copyright (c) 2020. Invoice Ninja LLC (https://invoiceninja.com)
+ *
+ * @license https://opensource.org/licenses/AAL
+ */
+
+namespace App\Http\ValidationRules\Recurring;
+
+use App\Libraries\MultiDB;
+use App\Models\Invoice;
+use App\Models\RecurringInvoice;
+use App\Models\User;
+use Illuminate\Contracts\Validation\Rule;
+
+/**
+ * Class UniqueRecurringInvoiceNumberRule.
+ */
+class UniqueRecurringInvoiceNumberRule implements Rule
+{
+    public $input;
+
+    public function __construct($input)
+    {
+        $this->input = $input;
+    }
+
+    /**
+     * @param string $attribute
+     * @param mixed $value
+     * @return bool
+     */
+    public function passes($attribute, $value)
+    {
+        return $this->checkIfInvoiceNumberUnique(); //if it exists, return false!
+    }
+
+    /**
+     * @return string
+     */
+    public function message()
+    {
+        return "Recurring Invoice number {$this->input['number']} already taken";
+    }
+
+    /**
+     * @param $email
+     *
+     * //off,when_sent,when_paid
+     *
+     * @return bool
+     */
+    private function checkIfInvoiceNumberUnique() : bool
+    {
+        if(empty($this->input['number']))
+            return true;
+
+        $invoice = RecurringInvoice::where('client_id', $this->input['client_id'])
+                        ->where('number', $this->input['number'])
+                        ->withTrashed()
+                        ->exists();
+
+        if ($invoice) {
+            return false;
+        }
+
+        return true;
+    }
+}