A method of initialising rendering at a graphics processing unit configured to perform safety-critical rendering within a graphics processing system, the method comprising: generating configuration data for initialising rendering of safety critical graphical data at the graphics processing unit; receiving the configuration data for initialising rendering at the graphics processing unit; configuring the graphics processing unit in accordance with the configuration data for initialising rendering; determining whether the graphics processing unit is correctly configured in accordance with the configuration data; and determining, by a safety controller external to the graphics processing unit, that an initialisation error has occurred in response to determining that the graphics processing unit is not correctly configured in accordance with the configuration data.