This Info Flash outlines the necessity to take a closer look at Russian-Belarusian military cooperation. While increased military cooperation between Russia and Belarus can be expected in an ongoing war, this depends on many more factors, and it is rather difficult to estimate its exact form. For the European Union, however, this cooperation poses a significant risk, and even though the involvement of the Belarusian army in the war seems unlikely, many factors at play can change this. The previously reached factors and many more factors are further discussed in this work, with the main research questions focusing on how close is the Belarus-Russian military cooperation and why it poses a threat to the European Union.