diff --git a/sale.py b/sale.py
index 0c09caf576..99745564c1 100644
--- a/sale.py
+++ b/sale.py
@@ -28,7 +28,7 @@ class Sale(metaclass=PoolMeta):
         weights = []
         context['weights'] = weights
 
-        lines = [l for l in self.lines or [] if l.quantity > 0]
+        lines = [l for l in self.lines or [] if l.quantity and l.quantity > 0]
         keyfunc = partial(self._group_parcel_key, lines)
         lines = sorted(lines, key=keyfunc)