A new outer bound for the two-user discrete memoryless interference channel is presented. This bound establishes the capacity region of the binary erasure interference channel, whose determination was left open in the work of Vanroose and van der Meulen (1991). The new bound is compared with the best known outer bounds for some additional examples. It is also shown that the new outer bound is tight for a one-sided deterministic interference channel that belongs to the class studied by El Gamal and Costa.