changing constraints

I tried adding a constraint thus:
de4=> ALTER TABLE genus ADD CHECK(gender = 'masculine' || 'feminine');
But get the msg:
ERROR:  AlterTableAddConstraint: rejected due to CHECK constraint $2

de4=> \d genus               Table "public.genus"    Column     |         Type          | Modifiers
----------------+-----------------------+-----------genus_name     | character varying(20) | not nullgender         |
charactervarying(10) |cas_gen_number | integer               |family_name    | character(7)          |
 
Indexes: genus_pkey primary key btree (genus_name)
Foreign Key constraints: $1 FOREIGN KEY (family_name) REFERENCES
family(family_name) ON UPDATE NO ACTION ON DELETE NO ACTION

I cant see a $2 constraint so why am i getting the error msg?

Many thanks Dave