As per https://www.ycombinator.com/deal “The $125k safe and the MFN safe will each convert into preferred shares when your company raises money by selling preferred shares in a priced equity round, which we refer to below as the “Safe Conversion Financing” (this will typically be your “Series A” or “Series Seed” financing, whichever happens first).”
Edit: Sorry, I am absolutely wrong here. I completely misunderstood what nirmel was saying.
You're just providing an alternate scenario that isn't as favorable. And since the initial $125k implicitly has a $2m valuation attached to it, if you raise again at $3.75m, then that's probably not ideal.
So a sensible approach would be to view this as providing an implicit minimum value to target for your next round, i.e., >$5m (7.5%).