M-theory is a candidate for a theory of quantum gravity. Its fundamental objects are called M2-branes and M5-branes. The low-energy theory describing coincident M5-branes is poorly understood in many respects, with holography providing one of the most useful tools to further that understanding. It is known that the theory should possess solitonic solutions called "self-dual strings". An important quantity characterising these strings is their central charge, which among other things counts the massless degrees of freedom on the string. I will describe configurations of M-branes dual to the insertion of infinite tension self-dual strings into the M5-brane theory, and how calculation of holographic entanglement entropy in such set-ups yields the central charge of the self-dual string.