Arrangements for network slice isolation. A method is performed by a terminal device. The method includes determining to shift from accessing a first service using a current network slice to accessing a second service using a target network slice. Network access to the current network slice is handled by a source Access Management Function. Network access to the target network slice is handled by a target Access Management Function. The method includes performing a slice authentication procedure in response thereto. During the authentication procedure a mutual secret is shared between the terminal device and the target Access Management Function. The method includes creating a security context for the target network slice based on the mutual secret. The method includes activating the security context, thereby security isolating the target network slice from the source Access Management Function.