Background: Mutation testing is the state-of-the-art technique for assessing the fault detection capacity of a test suite. Unfortunately, it is seldom applied in practice because it is computationally expensive. We witnessed 48 hours of mutation testing time on a test suite comprising 272 unit tests and 5,258 lines of test code for testing a project with 48,873 lines of production code. Aims: Therefore, researchers are currently investigating cloud solutions, hoping to achieve sufficient speed-up to allow for a complete mutation test run during the nightly build. Method: In this paper we evaluate mutation testing in the cloud against two industrial projects. Results: With our proof-of-concept, we achieved a speed-up between 12x and 12.7x on a cloud infrastructure with 16 nodes. This allowed to reduce the aforementioned 48 hours of mutation testing time to 3.7 hours. Conclusions: We make a detailed analysis of the delays induced by the distributed architecture, point out avenues for further optimisation and elaborate on the lessons learned for the mutation testing community. Most importantly, we learned that for optimal deployment in a cloud infrastructure, tasks should remain completely independent. Mutant optimisation techniques that violate this principle will benefit less from deploying in the cloud.