diff --git a/Rakefile b/Rakefile
index 3b5a3c1..67175f5 100644
--- a/Rakefile
+++ b/Rakefile
@@ -548,7 +548,7 @@ targets.each do |target|
                 end
                 line << unit_price
                 line << total_price
-                sum[seller_i][boards_i] += line[-1]
+                sum[seller_i][boards_i] += (line[-1] || 0.0)
                 stocks[seller_i][boards_i] &= (quantity<=price["in_stock_quantity"])
               end
             else # no price available