During engine braking of a turbocharged internal combustion engine, the exhaust gas pressure increases and this is used to pressurize the seals between the turbocharger shaft and the bearing housing so as to prevent oil leakage into the compressor housing. Immediately after engine braking, stored exhaust gas pressure is used to pressurize the seals at the turbine end so as to prevent oil leakage into the turbine housing. In an alternative arrangement the exhaust gas is used to generate a reduced pressure in the bearing housing to increase the pressure gradient across the seals.