diff --git a/src/simpleRdf/Dataset.php b/src/simpleRdf/Dataset.php
index bb40e9b..5daa7ec 100644
--- a/src/simpleRdf/Dataset.php
+++ b/src/simpleRdf/Dataset.php
@@ -384,7 +384,8 @@ private function listQuadElement(iQuadCompare | iQuadIterator | callable | null
                                      string $elementFn): Generator {
         try {
             $spotted = [];
-            $idx     = $this->findMatchingQuads($filter);
+            // materialize to avoid problems with parallel quads iterations
+            $idx     = iterator_to_array($this->findMatchingQuads($filter));
             foreach ($idx as $i) {
                 $i    = $this->quads[$i]->$elementFn();
                 $flag = true;