diff --git a/Chapter11/myshop/cart/cart.py b/Chapter11/myshop/cart/cart.py
index a0015c7a..eafeb620 100644
--- a/Chapter11/myshop/cart/cart.py
+++ b/Chapter11/myshop/cart/cart.py
@@ -73,6 +73,9 @@ def remove(self, product):
     def clear(self):
         # remove cart from session
         del self.session[settings.CART_SESSION_ID]
+
+        # remove used coupon from session
+        del self.session['coupon_id']
         self.save()
 
     def get_total_price(self):