How important is form on heavy deadlifts?

[Viktor]

Yesterday I did 1*5 on 155kg deadlift
On the fourth rep my mate told me my back was rounding a bit
It did so as well on 150, but 152.5 was fine.

I read in your book SS that many heavy deadlifts had been missed this way.

Would you recommend me to increase the weight for next time or back off and not accept poor form?

[Mark Rippetoe]

Were the three sets you described above done in the same workout?

[Viktor]

No different work outs

I usually do

5*60kg/ 3*100/ 2* 137.5/ workset

[Mark Rippetoe]

At limit weights form will break down a little. If it breaks down a lot, the load is too high and has revealed a hole in your preparation that should be filled.