diff --git a/ereuse_devicehub/inventory/forms.py b/ereuse_devicehub/inventory/forms.py
index 00fe0240..d8677dd2 100644
--- a/ereuse_devicehub/inventory/forms.py
+++ b/ereuse_devicehub/inventory/forms.py
@@ -46,9 +46,11 @@ class LotDeviceForm(FlaskForm):
             return False
 
         self._lot = (
-            Lot.query.filter(Lot.id == self.lot.data)
-            .filter(Lot.owner_id == g.user.id)
-            .one()
+            Lot.query.outerjoin(Trade)
+            .filter(Lot.id == self.lot.data)
+            .filter(or_(Trade.user_from == g.user,
+                        Trade.user_to == g.user,
+                        Lot.owner_id == g.user.id)).one()
         )
 
         devices = set(self.devices.data.split(","))
@@ -68,14 +70,16 @@ class LotDeviceForm(FlaskForm):
                 if trade not in dev.actions:
                     trade.devices.add(dev)
 
-        self._lot.devices.update(self._devices)
-        db.session.add(self._lot)
-        db.session.commit()
+        if self._devices:
+            self._lot.devices.update(self._devices)
+            db.session.add(self._lot)
+            db.session.commit()
 
     def remove(self):
-        self._lot.devices.difference_update(self._devices)
-        db.session.add(self._lot)
-        db.session.commit()
+        if self._devices:
+            self._lot.devices.difference_update(self._devices)
+            db.session.add(self._lot)
+            db.session.commit()
 
 
 class LotForm(FlaskForm):
diff --git a/ereuse_devicehub/inventory/views.py b/ereuse_devicehub/inventory/views.py
index c0059183..62cd97cb 100644
--- a/ereuse_devicehub/inventory/views.py
+++ b/ereuse_devicehub/inventory/views.py
@@ -135,9 +135,14 @@ class LotDeviceAddView(View):
         form = LotDeviceForm()
         if form.validate_on_submit():
             form.save()
+            messages.success(
+                'Add devices to lot "{}" successfully!'.format(form._lot.name)
+            )
+        else:
+            messages.error('Error adding devices to lot!')
 
-            next_url = request.referrer or url_for('inventory.devices.devicelist')
-            return flask.redirect(next_url)
+        next_url = request.referrer or url_for('inventory.devices.devicelist')
+        return flask.redirect(next_url)
 
 
 class LotDeviceDeleteView(View):
@@ -149,9 +154,14 @@ class LotDeviceDeleteView(View):
         form = LotDeviceForm()
         if form.validate_on_submit():
             form.remove()
+            messages.success(
+                'Remove devices from lot "{}" successfully!'.format(form._lot.name)
+            )
+        else:
+            messages.error('Error removing devices from lot!')
 
-            next_url = request.referrer or url_for('inventory.devices.devicelist')
-            return flask.redirect(next_url)
+        next_url = request.referrer or url_for('inventory.devices.devicelist')
+        return flask.redirect(next_url)
 
 
 class LotCreateView(View):