diff --git a/app/Ninja/Import/BaseTransformer.php b/app/Ninja/Import/BaseTransformer.php
index 6f91fe5336a3..2f0131c9dfa7 100644
--- a/app/Ninja/Import/BaseTransformer.php
+++ b/app/Ninja/Import/BaseTransformer.php
@@ -143,7 +143,7 @@ class BaseTransformer extends TransformerAbstract
      */
     protected function getInvoiceNumber($number)
     {
-        return str_pad($number, 4, '0', STR_PAD_LEFT);
+        return str_pad(trim($number), 4, '0', STR_PAD_LEFT);
     }
 
     /**
@@ -153,6 +153,7 @@ class BaseTransformer extends TransformerAbstract
     protected function getInvoiceId($invoiceNumber)
     {
         $invoiceNumber = $this->getInvoiceNumber($invoiceNumber);
+        $invoiceNumber = strtolower($invoiceNumber);
         return isset($this->maps[ENTITY_INVOICE][$invoiceNumber]) ? $this->maps[ENTITY_INVOICE][$invoiceNumber] : null;
     }
 
@@ -163,6 +164,7 @@ class BaseTransformer extends TransformerAbstract
     protected function hasInvoice($invoiceNumber)
     {
         $invoiceNumber = $this->getInvoiceNumber($invoiceNumber);
+        $invoiceNumber = strtolower($invoiceNumber);
         return isset($this->maps[ENTITY_INVOICE][$invoiceNumber]);
     }
 
@@ -173,6 +175,7 @@ class BaseTransformer extends TransformerAbstract
     protected function getInvoiceClientId($invoiceNumber)
     {
         $invoiceNumber = $this->getInvoiceNumber($invoiceNumber);
+        $invoiceNumber = strtolower($invoiceNumber);
         return isset($this->maps[ENTITY_INVOICE.'_'.ENTITY_CLIENT][$invoiceNumber])? $this->maps[ENTITY_INVOICE.'_'.ENTITY_CLIENT][$invoiceNumber] : null;
     }