This paper describes an incident of inadvertent radiation exposure to a cleaner who had entered a linac bunker maze during maintenance work on the linac. In fact, the cleaner was not exposed to the primary beam, and subsequent physics assessment indicated any radiation dose received was likely to have been close to background levels. However, the situation illustrates the potential for much more serious inadvertent radiation exposures and raises considerations for both type, and physical positions, of the interlocks that control the Beam-On and operator-acknowledgement of a cleared Linac room; and also of the operational procedures in relation to interlocked doors/gates and last-man-out buttons.