CREATE TYPE dow AS ENUM (
  'Monday', 'Tuesday', 'Wednesday', 'Thursday',
  'Friday', 'Saturday', 'Sunday'
);

CREATE TABLE available (
  dow      dow,
  tsrange  tsrange,
  EXCLUDE USING gist (tsrange WITH =, dow WITH &&)
);

ERROR:  data type dow 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.