Uising psql with String variable that has two periods

psql -d mydb -U me -h localhost -f db_log.sql -v db_user_string='Me' -v version="1.7.3"

into the script

begin;
create table db_log (db_owner varchar(255) not null, db_user varchar(255) not null, version varchar(255) not null, created timestamp, id serial primary key);
insert into db_log (db_owner, db_user, version, created) VALUES (current_user, :db_user_string, :version, current_timestamp);
commit;

gives...

psql:db_log.sql:10: ERROR:  syntax error at or near ".3"

Any ideas?

I am using 9.3.0