News feeds in virtually all social media platforms include engagement metrics, such as the number of times each post is liked and shared. We find that exposure to these signals increases the vulnerability of users to low-credibility information in a simulated social media feed. This finding has important implications for the design of social media interactions in the post-truth age. To reduce the spread of misinformation, we call for technology platforms to rethink the display of social engagement metrics. Further research is needed to investigate how engagement metrics can be presented without amplifying the spread of low-credibility information.