pkg-config fails for www/serf

[Maho NAKATA]

Hi maintainer of /usr/ports/www/serf

When I tried following, I encountered the following error.
Could you please fix?
 
$ pkg-config --cflags --exists "serf-1 >= 1.1"
Package libssl was not found in the pkg-config search path.
Perhaps you should add the directory containing `libssl.pc'
to the PKG_CONFIG_PATH environment variable
No package 'libssl' found

Thanks
-- Nakata Maho http://accc.riken.jp/maho/ , JA OOO http://ja.openoffice.org/
http://blog.goo.ne.jp/nakatamaho/ ,GPG: http://accc.riken.jp/maho/maho.pgp.txt