[R] Having problems with the ifelse and negative numbers

[rsherry8]

Please consider the following two R statements:
     A =  runif(20, min=-1,max=1)
     ifelse( A < 0, sqrt(-A), A )

The second statement produces the following error message:
     rt(-A) : NaNs produced

I understand that you cannot take the square root of a negative number 
but I thought the condition A < 0
would take care of that issue. It appears not to be.

What am I missing?

Thanks,
Bob