Restrict access query

Hi all, I'm using Moodle 2.5.

I have set up my own grading scale (a simple pass/fail) for an assignment.

I want to restrict access to the next topic if a student receives a 'pass' for the current assignment. At the moment my Moodle only restricts grades based on percentages (e.g. 80% or higher). Is there a way to change it so the restrict access works with 'pass' or 'Pass' instead of numbers/percentages?

Many thanks, Jason