diff --git a/src/_port b/src/_port
index 11e91dd..064928a 100644
--- a/src/_port
+++ b/src/_port
@@ -70,6 +70,12 @@ _port() {
     '*:extra:->extra' \
     && return 0
 
+  local cache_policy
+  zstyle -s ":completion:${curcontext}:" cache-policy cache_policy
+  if [[ -z "$cache_policy" ]]; then
+    zstyle ":completion:${curcontext}:" cache-policy _port_caching_policy
+  fi
+
   case "$state" in
     extra)
       case "$words[2]" in
@@ -133,4 +139,11 @@ _port_select() {
   fi
 }
 
+_port_caching_policy() {
+  local reg_time comp_time
+  reg_time=$(stat -c '%Z' $port_prefix/var/macports/registry/registry.db)
+  comp_time=$(stat -c '%Z' $1)
+  return $(( reg_time < comp_time ))
+}
+
 _port "$@"