[Dovecot] Pigeonhole Sieve date extension

Probably I'm doing something stupidly wrong.

I have dovecot 1.2.7 and sieve 0.1.13. I have a sieve script starting with

# <some comment> require ["vacation", "date", "relational"];

I get

main_script: line 2: error: require command: unknown Sieve capability 'date'.

Just to make sure I haven't messed up the dovecot package:

$ strings /usr/pkg/lib/dovecot/lda/lib90_sieve_plugin.a | fgrep date_extension date_extension date_extension date_extension date_extension date_extension

What's going on? It's probably some totally stupid typo on my side.