rrdtool 1.5 'don't understand' my previously working CDEF

Hi,

I've been using rrdtool 1.4.x for years with a certain script, but I got 
into some issues when FreeBSD introduced 1.5.5 (1.4.8 before).
Basically, I have some temperature data, in which I want to filter out 
the exact value 85.00, and "render" an unkn/nan instead:

DEF:rawmax=myfile.rrd:value:MAX
CDEF:vmax=rawmax,85.00,EQ,NaN,rawmax,IF

Since the upgrade, rrdtool now fails with ERROR: don't understand 
'NaN,rawmax,IF'
I've checked again and again, but I fail to see any syntax errors or 
other apparent issues. I've tried with UNKN instead of NaN and other 
stuff, but no success..

If anyone could point me in the right direction I'd be very happy!

Thanks,
Johan