diff --git a/lib/icinga/notification.hpp b/lib/icinga/notification.hpp
index 1b6cbedb1..8c5a5f4b1 100644
--- a/lib/icinga/notification.hpp
+++ b/lib/icinga/notification.hpp
@@ -55,6 +55,7 @@ class ApplyRule;
 struct ScriptFrame;
 class Host;
 class Service;
+class UserGroup;
 
 /**
  * An Icinga notification specification.
@@ -73,7 +74,7 @@ public:
 	intrusive_ptr<NotificationCommand> GetCommand() const;
 	TimePeriod::Ptr GetPeriod() const;
 	std::set<User::Ptr> GetUsers() const;
-	std::set<UserGroup::Ptr> GetUserGroups() const;
+	std::set<intrusive_ptr<UserGroup>> GetUserGroups() const;
 
 	void UpdateNotificationNumber();
 	void ResetNotificationNumber();
diff --git a/lib/icinga/usergroup.hpp b/lib/icinga/usergroup.hpp
index c6f82a131..3435f6c16 100644
--- a/lib/icinga/usergroup.hpp
+++ b/lib/icinga/usergroup.hpp
@@ -4,6 +4,7 @@
 #define USERGROUP_H
 
 #include "icinga/i2-icinga.hpp"
+#include "icinga/notification.hpp"
 #include "icinga/usergroup-ti.hpp"
 #include "icinga/user.hpp"