diff --git a/src/Utils/DataRefReplacer.php b/src/Utils/DataRefReplacer.php
index df4214e..21be503 100644
--- a/src/Utils/DataRefReplacer.php
+++ b/src/Utils/DataRefReplacer.php
@@ -192,7 +192,7 @@ private function recursiveReplaceSelfClosedPcTags(object $node, string $string):
         } elseif ($node->tagName == 'pc' && $node->self_closed === true) {
             $attributesMap = Map::instance($node->attributes);
 
-            if ($dataRefStartValue = $this->map->get($node->attributes['dataRefStart'])) {
+            if (isset($node->attributes['dataRefStart']) && $dataRefStartValue = $this->map->get($node->attributes['dataRefStart'])) {
                 $string = $this->replaceNewTagString(
                     $node->node,
                     $attributesMap->get('id'),