Example implementations relate to standby controllers for access points (APs). A network controller may comprise a processing resource; and a memory resource storing machine-readable instructions to cause the processing resource to: determine, in response to a first controller in a controller cluster failing, whether a first AP managed by a first controller has been assigned to a standby controller; determine, in response to the first AP managed by the first controller not having a standby controller assigned, a radio frequency (RF) gap as a result of a different controller failing; and based on the size of the RF gap, assign the second controller as a standby controller for the first AP.