diff --git a/zmldapsync/zmldapsync.pl b/zmldapsync/zmldapsync.pl
index 618931e..981f4ec 100755
--- a/zmldapsync/zmldapsync.pl
+++ b/zmldapsync/zmldapsync.pl
@@ -562,16 +562,16 @@ DOMAIN: foreach my $domain ( keys $conf->{domains} ) {
                not defined $zim_dl->{$group}->{$conf->{domains}->{$domain}->{groups}->{attr_map}->{$attr}} ) {
             # Attr does not exist in external LDAP and in Zimbra, not need to continue
             next;
-          } elsif ( not defined $ext_groups->{$group}->{$attr} ) {
+          } elsif ( not defined $ext_groups->{$group}->{$attr} and defined $conf->{domains}->{$domain}->{groups}->{attr_map}->{$attr} ) {
             # Attr doesn't exist in external LDAP, but exists in Zimbra. We must remove it
             $attrs = ' -' . $conf->{domains}->{$domain}->{groups}->{attr_map}->{$attr} . " " .
                      zim_attr_value( $zim_dl->{$group}->{$conf->{domains}->{$domain}->{groups}->{attr_map}->{$attr}} );
-          } elsif ( $ext_groups->{$group}->{$attr} ne $zim_dl->{$group}->{$conf->{domains}->{$domain}->{groups}->{attr_map}->{$attr}} ) {
+          } elsif ( ( $ext_groups->{$group}->{$attr} || '' ) ne ( $zim_dl->{$group}->{$conf->{domains}->{$domain}->{groups}->{attr_map}->{$attr}} || '' ) ) {
             # Attr exists in both but doesn't match
-            $attrs .= " " . $conf->{domains}->{$domain}->{groups}->{attr_map}->{$attr} . " " .
+            $attrs .= " " . ( $conf->{domains}->{$domain}->{groups}->{attr_map}->{$attr} || '' ) . " " .
                       zim_attr_value( $ext_groups->{$group}->{$attr} );
-            log_verbose( $ext_groups->{$group}->{$attr} . " vs " .
-		         $zim_dl->{$group}->{$conf->{domains}->{$domain}->{groups}->{attr_map}->{$attr}} );
+            log_verbose( "Attribute $attr for group $group changed from " . ( $ext_groups->{$group}->{$attr} || 'an empty value' ) . " to " .
+		         ( $zim_dl->{$group}->{$conf->{domains}->{$domain}->{groups}->{attr_map}->{$attr}} || 'an empty value' ) );
           }
         }