  Using extended island formula we compute entanglement entropy of Hawking
radiation for black hole solutions of certain gravitational models containing
higher derivative terms. To be concrete we consider two different four
dimensional models to compute entropy for both asymptotically flat and AdS
black holes. One observes that the resultant entropy follows the Page curve,
thanks to the contribution of the island, despite the fact that the
corresponding gravitational models might be non-unitary.
