We present a clock-offset tracking algorithm for impulse-radio ultra-wide band (IR-UWB) energy-detection receivers. There is a complexity versus performance trade-off for the design of IR-UWB energy-detection receivers: Extremely low-complexity energy-detection receivers are built with a large, constant integration duration; they are robust to clock drifts but are sensitive to noise enhancement effects and cannot adapt to channel variations. More sophisticated energy-detection receivers use a shorter integration duration and combine several weighted outputs of the energy collector; they are robust to noise enhancement effects, can adapt to channel variations and offer a much better performance than non-adaptive receivers. However, they become sensitive to clock offsets. Hence, there is a need for low-complexity clock-offset tracking solutions to support adaptive energy-detection receivers. Our solution is constructed around the Radon transform, an image processing tool traditionally used to detect line features in images. Our solution is fully compatible with the IEEE 802.15.4a standard, does not increase the hardware complexity of the receiver and reduces the performance loss due to clock offset to less than 0.5 dB.