An internal combustion engine arrangement, comprising: - an internal combustion engine ; - an exhaust line collecting exhaust gases from the engine ; - an additional fluid line , distinct from the exhaust line , carrying a warm fluid; - a waste heat recovery system carrying a working fluid in a closed loop, in which said working fluid is successively pressurized from a low pressure circuit portion to a high pressure circuit portion by a pump , evaporated in the high pressure circuit portion, expanded in an expander from the high pressure circuit portion to a low pressure circuit portion, and condensed in a condenser in the low pressure circuit portion, the waste heat recovery system comprising a first and a second lines arranged in parallel in the high pressure circuit portion upstream of the expander , the first and second lines joining at a downstream junction point in the high pressure circuit portion upstream of the expander , wherein the first line comprises a first heat exchanger thermally connected to the exhaust line , in which the working fluid can be heated by means of the exhaust gases, and the second line comprises a second heat exchanger thermally connected to the additional fluid line , in which the working fluid can be heated by means of the warm fluid; characterized in that it further comprises: - a first by-pass system designed to prevent not fully evaporated working fluid from the first line to flow through the expander ; - a second by-pass system which connects the second line upstream of the downstream junction point , to the low pressure circuit portion, at a connecting point , for by-passing the downstream junction point and the expander . - an internal combustion engine ; - an exhaust line collecting exhaust gases from the engine ; - an additional fluid line , distinct from the exhaust line , carrying a warm fluid; - a waste heat recovery system carrying a working fluid in a closed loop, in which said working fluid is successively pressurized from a low pressure circuit portion to a high pressure circuit portion by a pump , evaporated in the high pressure circuit portion, expanded in an expander from the high pressure circuit portion to a low pressure circuit portion, and condensed in a condenser in the low pressure circuit portion, the waste heat recovery system comprising a first and a second lines arranged in parallel in the high pressure circuit portion upstream of the expander , the first and second lines joining at a downstream junction point in the high pressure circuit portion upstream of the expander , wherein the first line comprises a first heat exchanger thermally connected to the exhaust line , in which the working fluid can be heated by means of the exhaust gases, and the second line comprises a second heat exchanger thermally connected to the additional fluid line , in which the working fluid can be heated by means of the warm fluid; - a first by-pass system designed to prevent not fully evaporated working fluid from the first line to flow through the expander ; - a second by-pass system which connects the second line upstream of the downstream junction point , to the low pressure circuit portion, at a connecting point , for by-passing the downstream junction point and the expander . <EOS>