A hydraulic seal arrangement for a rotating machine, particularly a gas turbine engine, comprises a hydraulic seal and a hydraulic trap. When the machine is shut down, oil is retained in the hydraulic trap. When the machine is restarted, the oil from the hydraulic trap is available to re-make the hydraulic seal, thereby reducing or avoiding the leakage that typically occurs in such seal arrangements until the flow of oil through the seal arrangement is re-established.