diff --git a/library/Episciences/Paper.php b/library/Episciences/Paper.php
index 68a097c8..146c227e 100644
--- a/library/Episciences/Paper.php
+++ b/library/Episciences/Paper.php
@@ -5027,7 +5027,7 @@ public function getClassifications(bool $isSerialized = false): array
             $classificationName = $classification['classification_name'];
             if ($classificationName !== msc2020::$classificationName || $classificationName !== jel::$classificationName) {
                 $current = ($classificationName === msc2020::$classificationName) ? new msc2020($classification) : new jel($classification);
-                $classificationCollection[$classificationName] = !$isSerialized ? $current : $current->jsonSerialize(false);
+                $classificationCollection[$classificationName][] = !$isSerialized ? $current : $current->jsonSerialize(false);
             }
         }