diff --git a/tine20/Sales/Model/DocumentPosition/Abstract.php b/tine20/Sales/Model/DocumentPosition/Abstract.php
index d18c0db74c2..5c1bb7eb4e7 100644
--- a/tine20/Sales/Model/DocumentPosition/Abstract.php
+++ b/tine20/Sales/Model/DocumentPosition/Abstract.php
@@ -658,6 +658,10 @@ public function computePrice(bool $onlyProductType = true): void
             $discount = 0;
         }
 
+        if (null === $this->{self::FLD_SALES_TAX_RATE}) {
+            $this->{self::FLD_SALES_TAX_RATE} = Tinebase_Config::getInstance()->{Tinebase_Config::SALES_TAX};
+        }
+
         $total = is_null($this->{self::FLD_POSITION_PRICE}) ? null
             : $this->{self::FLD_POSITION_PRICE} - $discount;