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 (11, 12) arranged in parallel in the high pressure circuit portion upstream of the expander, the first and second lines (11, 12) 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 (11, 12) arranged in parallel in the high pressure circuit portion upstream of the expander, the first and second lines (11, 12) 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.