diff --git a/opac/opac-shelves.pl b/opac/opac-shelves.pl
index 237ad91cf1..3240506cf9 100755
--- a/opac/opac-shelves.pl
+++ b/opac/opac-shelves.pl
@@ -108,12 +108,12 @@ if ( $op eq 'add_form' ) {
         my $sortfield = $query->param('sortfield');
         $sortfield = 'title' unless grep {/^$sortfield$/}qw( title author copyrightdate itemcallnumber );
         if ( $shelf->can_be_managed( $loggedinuser ) ) {
-            $shelf->shelfname( $query->param('shelfname') );
+            $shelf->shelfname( scalar $query->param('shelfname') );
             $shelf->sortfield( $sortfield );
-            $shelf->allow_add( $query->param('allow_add') );
-            $shelf->allow_delete_own( $query->param('allow_delete_own') );
-            $shelf->allow_delete_other( $query->param('allow_delete_other') );
-            $shelf->category( $query->param('category') );
+            $shelf->allow_add( scalar $query->param('allow_add') );
+            $shelf->allow_delete_own( scalar $query->param('allow_delete_own') );
+            $shelf->allow_delete_other( scalar $query->param('allow_delete_other') );
+            $shelf->category( scalar $query->param('category') );
             eval { $shelf->store };
 
             if ($@) {