diff --git a/includes/solr_connection.inc b/includes/solr_connection.inc
index b8e5c9f..0c68057 100644
--- a/includes/solr_connection.inc
+++ b/includes/solr_connection.inc
@@ -908,7 +908,7 @@ class SearchApiSolrConnection implements SearchApiSolrConnectionInterface {
         $qalt = array();
         foreach ($params['fq'] as $i => $fq) {
           // Tagged and negative filters cannot be moved to q.alt.
-          if ($fq[0] !== '{' && $fq[0] !== '-') {
+          if (substr($fq[0], 0, 1) !== '{' && substr($fq[0], 0, 1) !== '-') {
             $qalt[] = "($fq)";
             unset($params['fq'][$i]);
           }