Heads up from our friends at Livesquawk to an article from Reuters

Standard and Poor's, Fitch and DBRS all say that as the IMF and ECB are not standard creditors, a missed payment to either, although likely to push Greece's rating even deeper into junk, would not be classed as a default.

Frank Gill, who rates Greece for S&P says

If Greece were, for whatever reason, not to make a payment to the IMF or ECB that would not constitute a default under our criteria as it is 'official' sector debt

As was seen during Greece's massive 2012 debt restructuring, only when all four of the main agencies -- Moody's is the other one -- declared Athens in default, did the ECB say it would not accept Greek bonds as ELA collateral.

Full story here