memcached 1.2.5 and libevent

On installing or upgrading to memcached 1.2.5 I'm getting the following error: checking for libevent directory... configure: error: libevent is required. You can get it from http://www.monkey.org/~provos/libevent/ If it's already installed, specify its path using --with- libevent=/dir/ LibEvent is installed: libevent @1.3e_0 (active) MacPorts 1.6 Mac OS 10.5.2 (Intel, MacBook Pro Core Duo) Martin