In this work, we present a novel method for ankle/foot compliance for biped humanoid robots walking over uneven terrain. Based on distributed plantar proximity sensing, we developed the Preemptive Foot Compliance (PFC) control that generates a Preemptive Ground Reaction Wrench that modifies the foot orientation to maximize the largest contact area to reduce the impact force produced at landing. PFC can be easily included in any walking controller for flat ground and become capable of walking on uneven terrains. The PFC was tested on two full-size humanoid robots running two different walking controllers, originally designed only for flat-ground walking. Both robots increase their capability to walk over uneven terrain and the walking impacts in flat grown were reduced by approximately 80%.