This patch is included upstream, see:
    <http://www.zsh.org/mla/workers/2010/msg00992.html>

Index: pkg-zsh/Completion/Unix/Command/_fuser
===================================================================
--- pkg-zsh.orig/Completion/Unix/Command/_fuser	2011-02-11 16:42:14.000000000 +0100
+++ pkg-zsh/Completion/Unix/Command/_fuser	2011-02-11 16:42:16.000000000 +0100
@@ -3,7 +3,7 @@
 local -a args arg1
 typeset -A opt_args
 
-if _pick_variant -c $words[1] psmisc=psmisc unix -V; then
+if _pick_variant -c $words[1] psmisc='(#i)psmisc' unix -V; then
 
   (( $+functions[_fuser_services] )) ||
   _fuser_services() {