Default operator class for data type boolean for access method gist is missing

I'm trying to define the following exclusion-constraint   alter table my_table 
add EXCLUDE USING gist(is_default WITH =, daterange(valid_from, valid_to, '[)') 
WITH&&) WHERE (is_default = true);   But it fails with: ERROR:  data type 
boolean has no default operator class for access method "gist"
 HINT:  You must specify an operator class for the index or define a default 
operator class for the data type.   I have the btree_gist extension installed.  
So, my question is; Is there an existing operator-class I can install to make 
this work, and if not - how do I make it?   I know I can change is_default to 
INTEGER and use 1 and 0, but I'd really like to use boolean for this.   Thanks. 
  --
 Andreas Joseph Krogh <andreak@officenet.no>      mob: +47 909 56 963
 Senior Software Developer / CTO - OfficeNet AS - http://www.officenet.no
 Public key: http://home.officenet.no/~andreak/public_key.asc