Nat. Methods 11, 545–548 (2014); published online 16 March 2014; corrected after print 3 June 2015

In the version of this article initially published, the authors claimed that with the tool cctbx.xfel, weak diffraction signals can be measured using fewer crystal specimens than are needed for the previously available program CrystFEL. However, there is not enough evidence to support this claim. The inaccurate statements have been corrected in the HTML and PDF versions of the article.