diff --git a/app/Http/Requests/Invoice/UpdateInvoiceRequest.php b/app/Http/Requests/Invoice/UpdateInvoiceRequest.php
index 35bb8e621f7d..15c1a57c4c19 100644
--- a/app/Http/Requests/Invoice/UpdateInvoiceRequest.php
+++ b/app/Http/Requests/Invoice/UpdateInvoiceRequest.php
@@ -49,7 +49,7 @@ class UpdateInvoiceRequest extends Request
 
         $rules['id'] = new LockedInvoiceRule($this->invoice);
 
-        if ($this->input('number')) {
+        if ($this->input('number') && strlen($this->input('number')) >= 1) {
             $rules['number'] = 'unique:invoices,number,'.$this->id.',id,company_id,'.$this->invoice->company_id;
         }