division by zero

I admit, I suck at math, but I really thought postgres would ERROR on
this:

foo=# select 1/0;
  ?column?
----------
         0
(1 row)

More surprising is that this does ERROR:
foo=# select 1/0.0;
ERROR:  division by zero on numeric

Is this a bug, or do I need to go back to high school algebra?  "Both"
is an acceptable answer.  :)

eric