In component-based safety-critical embedded systems it is crucial to determine the cause(s) of the violation of a safety property, be it to issue a precise alert, to steer the system into a safe state, or to determine liability of component providers. In this paper we present an approach to blame components based on a single execution trace violating a safety property P. The diagnosis relies on counterfactual reasoning (" what would have been the outcome if component C had behaved correctly? ") to distinguish component failures that actually contributed to the outcome from failures that had little or no impact on the violation of P.