diff --git a/mod/forum/db/upgrade.php b/mod/forum/db/upgrade.php
index 541e4c55b43..b17ad2d76d6 100644
--- a/mod/forum/db/upgrade.php
+++ b/mod/forum/db/upgrade.php
@@ -176,5 +176,12 @@ function xmldb_forum_upgrade($oldversion) {
     // Automatically generated Moodle v4.1.0 release upgrade line.
     // Put any upgrade step following this.
 
+    if ($oldversion < 2022112801) {
+        // Some very old discussions from early Moodle versions may have the usermodified set to zero.
+        $DB->execute("UPDATE {forum_discussions} SET usermodified = userid WHERE usermodified = 0");
+
+        upgrade_mod_savepoint(true, 2022112801, 'forum');
+    }
+
     return true;
 }
diff --git a/mod/forum/version.php b/mod/forum/version.php
index 4f719f56b26..b390dcf630d 100644
--- a/mod/forum/version.php
+++ b/mod/forum/version.php
@@ -24,6 +24,6 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$plugin->version   = 2022112800;       // The current module version (Date: YYYYMMDDXX).
+$plugin->version   = 2022112801;       // The current module version (Date: YYYYMMDDXX).
 $plugin->requires  = 2022111800;       // Requires this Moodle version.
 $plugin->component = 'mod_forum';      // Full name of the plugin (used for diagnostics)