An important cue in the evaluation of the credibility of online information is the source from which the information comes. Earlier, it has been hypothesized that the source of information is less important when one is familiar with the topic at hand. However, no conclusive results were found to confirm this hypothesis. In this study, we re-examine the relationship between the source of information and topic familiarity. In an experiment with Wikipedia articles with and without the standard Wikipedia layout, we showed that, contrary to our expectations, familiar users have less trust in the information when they know it comes from Wikipedia than when they do not know its source. For unfamiliar users, no differences were found. Moreover, source cues only influenced trust when the credibility of the information itself was ambiguous. These results are interpreted in the 3S-model of information trust.