diff --git a/src/_port b/src/_port
index db39c1f..064928a 100644
--- a/src/_port
+++ b/src/_port
@@ -15,23 +15,6 @@
 #
 # ------------------------------------------------------------------------------
 
-_port_select() {
-  if (( CURRENT == 3 )); then
-    _describe 'Port select options' select_options
-  elif (( CURRENT == 4 )); then
-    local select_group
-    select_group=()
-    for f in $port_prefix/etc/select/*; do
-      select_group+=$(basename $f)
-    done
-    _describe "Port select groups" select_group
-  elif [[ $CURRENT -eq 5 && $words[3] == '--set' ]]; then
-    local select_variants
-    select_variants=("${(f)$(port select --list $words[4] | sed -e '1 d' -e 's/^[ \t]*//' -e 's/ (active)$//')}")
-    _describe "Port select group $words[4] variants" select_variants
-  fi
-}
-
 _port() {
   # Variables for _argument
   typeset -A opt_args
@@ -87,6 +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
@@ -103,22 +92,28 @@ _port() {
           _call_function - _port_select
           ;;
         contents|deactivate|setrequested|space|uninstall|unsetrequested)
-          # Cache the list of all ports.
-          if (( ! $+_installed_ports )); then
-            _installed_ports=$(_call_program path-installed "port installed | cut -d ' ' -f 3")
+          # Cache the list of installed ports.
+          if ( [[ ${+_port_installed_packages} -eq 0 ]] || _cache_invalid PORT_INSTALLED_PACKAGES ) &&
+            ! _retrieve_cache PORT_INSTALLED_PACKAGES;
+          then
+            _port_installed_packages=( $(_call_program path-all "port echo all") )
+            _store_cache PORT_INSTALLED_PACKAGES _port_installed_packages
           fi
           _alternative \
-            "ports:Installed ports:($_installed_ports)" \
+            "ports:Installed ports:($_port_installed_packages)" \
             "pseudo-common:Common Pseudo-portnames:($pseudo_common)" \
             "pseudo-advanced:Advanced Pseudo-portnames:($pseudo_advanced)"
           ;;
         *)
           # Cache the list of all ports.
-          if (( ! $+_all_ports )); then
-            _all_ports=$(_call_program path-all "port echo all")
+          if ( [[ ${+_port_available_packages} -eq 0 ]] || _cache_invalid PORT_AVAILABLE_PACKAGES ) &&
+            ! _retrieve_cache PORT_AVAILABLE_PACKAGES;
+          then
+            _port_available_packages=( $(_call_program path-all "port echo all") )
+            _store_cache PORT_AVAILABLE_PACKAGES _port_available_packages
           fi
           _alternative \
-            "ports:Available ports:($_all_ports)" \
+            "ports:Available ports:($_port_available_packages)" \
             "pseudo-common:Common Pseudo-portnames:($pseudo_common)" \
             "pseudo-advanced:Advanced Pseudo-portnames:($pseudo_advanced)"
           ;;
@@ -127,4 +122,28 @@ _port() {
   esac
 }
 
+_port_select() {
+  if (( CURRENT == 3 )); then
+    _describe 'Port select options' select_options
+  elif (( CURRENT == 4 )); then
+    local select_group
+    select_group=()
+    for f in $port_prefix/etc/select/*; do
+      select_group+=$(basename $f)
+    done
+    _describe "Port select groups" select_group
+  elif [[ $CURRENT -eq 5 && $words[3] == '--set' ]]; then
+    local select_variants
+    select_variants=("${(f)$(port select --list $words[4] | sed -e '1 d' -e 's/^[ \t]*//' -e 's/ (active)$//')}")
+    _describe "Port select group $words[4] variants" select_variants
+  fi
+}
+
+_port_caching_policy() {
+  local reg_time comp_time
+  reg_time=$(stat -c '%Z' $port_prefix/var/macports/registry/registry.db)
+  comp_time=$(stat -c '%Z' $1)
+  return $(( reg_time < comp_time ))
+}
+
 _port "$@"