diff -u b/commerce_vat.module b/commerce_vat.module
--- b/commerce_vat.module
+++ b/commerce_vat.module
@@ -347,10 +347,13 @@
          $component['price']['amount'] -= $amount_to_reduce_current;
          $amount_to_reduce_left -= $amount_to_reduce_current;
        }
-       // Remaining rounding difference deliberately reduces first nonzero component.
-       $nonzero_components[0]['price']['amount'] -= $amount_to_reduce_left;
-       $wrapper->commerce_unit_price->data = $data;
-       $included = TRUE;
+       // Change components only if there was a nonzero-one.
+       if (!empty($nonzero_components)) {
+         // Remaining rounding difference deliberately reduces first nonzero component.
+         $nonzero_components[0]['price']['amount'] -= $amount_to_reduce_left;
+         $wrapper->commerce_unit_price->data = $data;
+         $included = TRUE;
+       }
      }
      else {
        // Include the vat amount in the displayed unit price.