diff --git a/Solr_Base_Query.php b/Solr_Base_Query.php
index 8451527..e19b491 100644
--- a/Solr_Base_Query.php
+++ b/Solr_Base_Query.php
@@ -601,9 +601,10 @@ class SolrBaseQuery extends SolrFilterSubQuery implements DrupalSolrQueryInterfa
   public function getSolrsortUrlQuery() {
     $queryvalues = array();
     $solrsort = $this->solrsort;
+    $map = array_flip($this->field_map);
     if ($solrsort && ($solrsort['#name'] != 'score')) {
-      if (isset($this->field_map[$solrsort['#name']])) {
-        $solrsort['#name'] = $this->field_map[$solrsort['#name']];
+      if (isset($map[$solrsort['#name']])) {
+        $solrsort['#name'] = $map[$solrsort['#name']];
       }
       $queryvalues['solrsort'] = $solrsort['#name'] . ' ' . $solrsort['#direction'];
     }