diff --git a/src/Snowplow/RefererParser/Parser.php b/src/Snowplow/RefererParser/Parser.php
index 0c8931d..d7687c6 100644
--- a/src/Snowplow/RefererParser/Parser.php
+++ b/src/Snowplow/RefererParser/Parser.php
@@ -50,7 +50,7 @@ public function parse($refererUrl, $pageUrl = null)
 
         $searchTerm = null;
         if ($referer['parameters']) {
-            parse_str($refererParts['query'], $queryParts);
+            parse_str($refererParts['query']??'', $queryParts);
             foreach ($referer['parameters'] as $parameter) {
                 $searchTerm = isset($queryParts[$parameter]) ? $queryParts[$parameter] : $searchTerm;
             }