diff --git a/lib/db/install.xml b/lib/db/install.xml
index b3fea5c3a98..cc89357d8d1 100644
--- a/lib/db/install.xml
+++ b/lib/db/install.xml
@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8" ?>
-<XMLDB PATH="lib/db" VERSION="20251205" COMMENT="XMLDB file for core Moodle tables"
+<XMLDB PATH="lib/db" VERSION="20251208" COMMENT="XMLDB file for core Moodle tables"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:noNamespaceSchemaLocation="../../lib/xmldb/xmldb.xsd"
 >
@@ -3523,6 +3523,7 @@
       <INDEXES>
         <INDEX NAME="nextruntime_idx" UNIQUE="false" FIELDS="nextruntime"/>
         <INDEX NAME="timestarted_idx" UNIQUE="false" FIELDS="timestarted"/>
+        <INDEX NAME="nextruntime_classname" UNIQUE="false" FIELDS="nextruntime, classname"/>
       </INDEXES>
     </TABLE>
     <TABLE NAME="task_log" COMMENT="The log table for all tasks">
diff --git a/lib/db/upgrade.php b/lib/db/upgrade.php
index d36a746273b..522c4600608 100644
--- a/lib/db/upgrade.php
+++ b/lib/db/upgrade.php
@@ -1952,5 +1952,19 @@ function xmldb_main_upgrade($oldversion) {
         upgrade_main_savepoint(true, 2025041404.06);
     }
 
+    if ($oldversion < 2025041404.08) {
+        // Define index nextruntime_classname (not unique) to be added to task_adhoc.
+        $table = new xmldb_table('task_adhoc');
+        $index = new xmldb_index('nextruntime_classname', XMLDB_INDEX_NOTUNIQUE, ['nextruntime', 'classname']);
+
+        // Conditionally launch add index nextruntime_classname.
+        if (!$dbman->index_exists($table, $index)) {
+            $dbman->add_index($table, $index);
+        }
+
+        // Main savepoint reached.
+        upgrade_main_savepoint(true, 2025041404.08);
+    }
+
     return true;
 }