diff --git a/lib/plugins/acts_as_watchable/lib/acts_as_watchable.rb b/lib/plugins/acts_as_watchable/lib/acts_as_watchable.rb
index c284af38d..4ce3bb4a1 100644
--- a/lib/plugins/acts_as_watchable/lib/acts_as_watchable.rb
+++ b/lib/plugins/acts_as_watchable/lib/acts_as_watchable.rb
@@ -46,7 +46,7 @@ module Redmine
         # Removes user from the watchers list
         def remove_watcher(user)
           return nil unless user && user.is_a?(User)
-          Watcher.delete_all "watchable_type = '#{self.class}' AND watchable_id = #{self.id} AND user_id = #{user.id}"
+          watchers.where(:user_id => user.id).delete_all
         end
 
         # Adds/removes watcher