A method for making a lithographic printing plate is disclosed which comprises the steps of: (1) providing a heat-sensitive lithographic printing plate precursor comprising on a support having a hydrophilic surface or which is provided with a hydrophilic layer, a heat-sensitive coating, (2) image-wise exposing said precursor with IR-radiation or heat, and (3) developing said image-wise exposed precursor with an alkaline developing solution, characterised in that a sludge inhibiting agent is present in said precursor or in said developing solution or in said precursor and said developing solution, and wherein said sludge inhibiting agent is a triazaindolisine compound. According to the above method, the formation of sludge is inhibited or reduced.