A lithographic apparatus (100) includes a patterning device support structure (104) configured to support a patterning device (110), a gas inlet (116) configured to provide a gas flow (114) across a surface of the patterning device, and a temperature conditioning device (134) configured to condition the temperature of the gas flow based on a set point. The apparatus also includes a sensor (132) configured to measure a parameter indicative of an amount of heat added to at least one of the patterning device and a volume (126) between the patterning device and a lens (124) of a projection system (106) during operational use of the lithographic system. Further, the apparatus includes a controller (130) operatively coupled to the sensor and configured to adjust the set point based on the parameter measured by the sensor to control a temperature of the patterning device.