diff --git a/CHANGELOG.md b/CHANGELOG.md
index e9641a42b..d146a3a09 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## next deploy
 
+- Fix a bug: validator of reservation can't find if slot has reserved by reservable type
+
 ## v5.4.8 2022 June 29
 
 - My reservations dashboard
diff --git a/app/models/cart_item/reservation.rb b/app/models/cart_item/reservation.rb
index 363a21da7..9f9909217 100644
--- a/app/models/cart_item/reservation.rb
+++ b/app/models/cart_item/reservation.rb
@@ -50,8 +50,8 @@ class CartItem::Reservation < CartItem::BaseItem
       end
 
       if availability.available_type == 'machines'
-        s = Slot.find_by(start_at: slot[:start_at], end_at: slot[:end_at], availability_id: slot[:availability_id], canceled_at: nil)
-        unless s.nil?
+        s = Slot.includes(:reservations).where(start_at: slot[:start_at], end_at: slot[:end_at], availability_id: slot[:availability_id], canceled_at: nil, "reservations.reservable": @reservable)
+        unless s.empty?
           @errors[:slot] = 'slot is reserved'
           return false
         end