The COVID-19 pandemic resulted in millions of deaths. Despite an unparalleled collaborative research effort that led to effective vaccines and therapies being produced in record-breaking time, a complete understanding of the structure and lifecycle of the coronavirus known as SARS-CoV-2 is still lacking. Scientists used the biolabs and the SPB/SFX instrument at the European XFEL to study the main protease, or Mpro, of the virus to understand how it protects itself from oxidative damage. The results add key knowledge to our understanding of the workings of SARS-CoV-2 and the field of viral biology.