diff --git a/zmldapsync/zmldapsync.pl b/zmldapsync/zmldapsync.pl
index 5cb93c4..7a8be89 100644
--- a/zmldapsync/zmldapsync.pl
+++ b/zmldapsync/zmldapsync.pl
@@ -597,7 +597,11 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
 
       if ( not yaml_bool( $conf->{domains}->{$domain}->{groups}->{members_as_dn} ) ) {
         # If members are not listed as full DN, but by uid, simply concat it with the domain
-        foreach my $member ( $ext_groups->{$group}->{$conf->{domains}->{$domain}->{groups}->{members_attr}} ) {
+        foreach my $member ( @{ $ext_groups->{$group}->{$conf->{domains}->{$domain}->{groups}->{members_attr}} } ) {
+          if ( not defined $ext_users->{$member} ) {
+            log_verbose( "Skiping member $member of group $group as it doesn't match a Zimbra user" );
+            next;
+          }
           next if ( not defined $ext_users->{$member} and
                     not defined $ext_groups->{$member} );
           push @ext_members, $member . '@' . $domain;