diff --git a/core/DataTable.php b/core/DataTable.php
index 5049191c27e..f03969f6728 100644
--- a/core/DataTable.php
+++ b/core/DataTable.php
@@ -751,7 +751,7 @@ public function rebuildIndex()
         foreach ($this->rows as $id => $row) {
             $label = $row->getColumn('label');
             if ($label !== false) {
-                $this->rowsIndexByLabel[$label] = $id;
+                $this->rowsIndexByLabel[(string) $label] = $id;
             }
         }
 
@@ -830,7 +830,7 @@ public function addRow(Row $row)
         ) {
             $label = $row->getColumn('label');
             if ($label !== false) {
-                $this->rowsIndexByLabel[$label] = count($this->rows) - 1;
+                $this->rowsIndexByLabel[(string) $label] = count($this->rows) - 1;
             }
         }
         return $row;