There is a new EEP that suggests a way to show additional information about why a call to a BIF failed. Here is the EEP: https://github.com/erlang/eep/blob/master/eeps/eep-0054.md And here is the pull request for the implementation: https://github.com/erlang/otp/pull/2849 /Björn -- Björn Gustavsson, Erlang/OTP, Ericsson AB