On the surface it certainly sounds like good news. Petro Poroshenko and Vladimir Putin huddled with the leaders of France and Germany for seventeen hours and emerged a little while ago saying that a ceasefire between Ukraine and Russian “separatists” would begin on Sunday, followed by the withdrawal of heavy weapons. As with many such things, the details are a bit on the vague side and it’s difficult to simply assume that everyone currently fighting in the streets is going to abide by it.

The leaders of Germany, France, Russia and Ukraine have agreed a deal to end fighting in eastern Ukraine, participants at the summit talks said on Thursday.

The deal reached after all-night negotiations in the Belarussian capital Minsk included a ceasefire that would come into effect on Feb. 15, followed by the withdrawal of heavy weapons.

The news came as Ukraine was offered a $40-billion lifeline by the International Monetary Fund to stave off financial collapse.

The Minsk summit agreement offered hope for eastern Ukraine, German Chancellor Angela Merkel’s spokesman said.

If this actually happens (and holds) that’s great. We can all send our thanks to Hollande and Merkel for a job well done and give the combatants some space to start putting the pieces back together. But while I don’t want to jinx anything here, color me skeptical.

There are a few things which hold me back from too much optimism here and the first one can be summed up in two words: Vladimir Putin. Any deal with Putin relies on the credibility of his word. Fool me once, shame on you. Fool me 7,259 times, fire me and get a new negotiator.

Second, but related to Vlad, is the point I alluded to above. It’s fine for four world leaders to say that a deal has been reached, but that doesn’t mean anything if the people on the ground with the actual guns aren’t on board with the plan. Hasn’t Putin repeatedly told us that the “separatists” attacking the Ukrainians aren’t regular Russian forces and are not under his control? I’m not saying that anyone should be foolish enough to believe that, but it’s the perfect excuse for the ceasefire to mysteriously “fail” shortly after it begins.

And finally there is the timing. It may come as no surprise that there is an EU summit scheduled in Brussels which begins today and additional sanctions against Putin are up for discussion. Having just signed off on a ceasefire is certainly a convenient chip to have on the table for Putin at such a juncture. It will put pressure on the European leaders to “reward” him by not piling on more financial punishment, and if they do it anyway then he has an excuse to say the ceasefire is pointless because everyone is against him anyway.

None of this begins until Sunday so we’ll have to wait and see. Who knows? Perhaps Putin will prove me wrong, which would come as an unexpected and pleasant surprise.