Nature 529, 502–504 (2016); doi:10.1038/nature16493

Following publication of this Letter, we were made aware that the target cluster identified as ‘NGC 1696’ is instead the cluster ‘NGC 1806’. This mistake was caused by a misidentification in the Hubble Space Telescope image headers provided by the ESA Hubble Science Archive ( As a consequence, all occurrences of ‘NGC 1696’ in the Letter should be replaced by ‘NGC 1806’. The occurrence of ‘NGC 1806’ in the final paragraph of the main text should be removed. The mass of NGC 1806 should be 1.1 × 105 solar masses rather than 5.0 × 104 solar masses and ref. 1 should be cited. The sentence “Note that our NGC 1696 mass is based on extrapolation...adopting a Kroupa-like initial mass distribution.” should be deleted. Because none of these corrections relate to any scientific results in the Letter, there are no scientific implications for the results and conclusions. The online version has not been corrected.