diff --git a/src/Calc/Calc.php b/src/Calc/Calc.php
index 481b2e5..4c728b3 100644
--- a/src/Calc/Calc.php
+++ b/src/Calc/Calc.php
@@ -115,7 +115,7 @@ class Calc
                             $p = 0;
 
                             eval('@$p = ' . $formel . ';');
-                            if($p > 0) {
+                            if($p > 0 || $p < 0) {
                                 $price += $p;
                             }