Sven, Yep, looks like a bug to me, too. I've committed a fix --- changed if (s1 == 0 || s2 == 0) to if (s1 == 0 && s2 == 0). This should be safe, though perhaps not worth the bother. Upgraded the Coin library unitTest while I was at it, to test for proper operation of binaryOp with empty vectors. Lou