diff --git a/brmbar3/brmbar/Shop.py b/brmbar3/brmbar/Shop.py
index c219be1..fcc54be 100644
--- a/brmbar3/brmbar/Shop.py
+++ b/brmbar3/brmbar/Shop.py
@@ -126,9 +126,12 @@ class Shop:
         #self.withdraw_credit(amount, userfrom)
 
     def buy_for_cash(self, item, amount = 1):
+        iamount = int(amount)
+        famount = float(iamount)
+        assert famount == amount, "amount is not integer value %s".format(amount)
         cost = self.db.execute_and_fetch(
             "SELECT public.buy_for_cash(%s, %s, %s, %s, %s)",
-            [self.cash.id, item.id, amount, self.currency.id, item.name]
+            [self.cash.id, item.id, iamount, self.currency.id, item.name]
         )[0]
         # Buy: Currency conversion from item currency to shop currency
         #(buy, sell) = item.currency.rates(self.currency)