diff --git a/application/controllers/receivings.php b/application/controllers/receivings.php
index f49c49386..4b8f6a776 100644
--- a/application/controllers/receivings.php
+++ b/application/controllers/receivings.php
@@ -344,7 +344,7 @@ class Receivings extends Secure_area
 				'supplier_id' => $this->input->post('supplier_id') ? $this->input->post('supplier_id') : null,
 				'employee_id' => $this->input->post('employee_id'),
 				'comment' => $this->input->post('comment'),
-				'invoice_number' => $this->input->post('invoice_number')
+				'invoice_number' => $this->input->post('invoice_number') != '' ? $this->input->post('invoice_number') : null
 		);
 	
 		if ($this->Receiving->update($receiving_data, $receiving_id))
diff --git a/application/models/item.php b/application/models/item.php
index 7b18032fb..7025e1294 100644
--- a/application/models/item.php
+++ b/application/models/item.php
@@ -614,7 +614,7 @@ class Item extends CI_Model
 		$old_total_quantity = $this->db->get()->row()->quantity;
 
 		$total_quantity = $old_total_quantity + $items_received;
-		$average_price = ($items_received * $new_price + $old_total_quantity * $old_price)/$total_quantity;
+		$average_price = bcdiv(bcadd(bcmul($items_received, $new_price), bcmul($old_total_quantity, $old_price)), $total_quantity);
 
 		$data = array('cost_price' => $average_price);