To provide a two-stroke uniflow scavenging crosshead internal combustion engine having a plurality of cylinders.SOLUTION: A two-stroke uniflow scavenging internal combustion engine 100 having a plurality of cylinders 101, is configured to inject fuel gas into each of the plurality of cylinders 101 via a fuel gas supply system that is fluidically connectable to a fuel gas tank. The fuel gas supply system includes a first group of fuel gas valves 105 configured to inject the fuel gas into the cylinder during a compression stroke for each cylinder 101, allows the fuel gas to mix with the scavenging, and allows the mixture of scavenging and fuel gas to be compressed before being ignited. The fuel gas supply system further includes a safety valve 112 provided for each cylinder 101 at an upstream side of the first group of fuel gas valves 105, and the first group of fuel gas valves 105 are fluidically connectable to the fuel gas tank via the safety valve 112.SELECTED DRAWING: Figure 1