diff --git a/reportbuilder/classes/table/custom_report_table.php b/reportbuilder/classes/table/custom_report_table.php
index b2fb68c3b87..d25ef908683 100644
--- a/reportbuilder/classes/table/custom_report_table.php
+++ b/reportbuilder/classes/table/custom_report_table.php
@@ -338,7 +338,7 @@ class custom_report_table extends base_report_table {
             $buttonicon = html_writer::tag('i', '', ['class' => 'fa fa-angle-down']);
 
             // We need a cleaned version (without tags/entities) of the first row column to use as toggle button.
-            $rowfirstcolumn = strip_tags(reset($row));
+            $rowfirstcolumn = strip_tags((string) reset($row));
             $buttontitle = $rowfirstcolumn !== ''
                 ? get_string('showhide', 'core_reportbuilder', html_entity_decode($rowfirstcolumn, ENT_COMPAT))
                 : get_string('showhidecard', 'core_reportbuilder');