Nature 472, 454–457 (2011)

In Table 1 of this Letter, rows 9 and 10 ([Y/Fe] and [Sr/Fe]) were inadvertently switched for stars number 2, 3 and 4. In addition, the [Y/Fe] value for star number 3 should be +1.50 and not +1.55. The correct Table 1 is shown below, and this also now includes the [Fe/H] values for each of the studied stars (taken from ref. 1 (ref. 4 in the original Letter)). The typical uncertainty in the [Fe/H] values is 0.2 dex. Table 1 has been corrected in the HTML and PDF version of the manuscript.

Table 1 Abundances of the eight stars in NGC 6522.