diff --git a/libraries/classes/Controllers/Table/ReplaceController.php b/libraries/classes/Controllers/Table/ReplaceController.php
index fd3f827d69..365d13a3b9 100644
--- a/libraries/classes/Controllers/Table/ReplaceController.php
+++ b/libraries/classes/Controllers/Table/ReplaceController.php
@@ -363,10 +363,11 @@ final class ReplaceController extends AbstractController
                 $value_sets[] = implode(', ', $query_values);
             } else {
                 // build update query
+                $clauseIsUnique = $_POST['clause_is_unique'] ?? '';// Should contain 0 or 1
                 $query[] = 'UPDATE ' . Util::backquote($table)
                     . ' SET ' . implode(', ', $query_values)
                     . ' WHERE ' . $where_clause
-                    . ($_POST['clause_is_unique'] ? '' : ' LIMIT 1');
+                    . ($clauseIsUnique ? '' : ' LIMIT 1');
             }
         }
         unset(