diff --git a/lib/db/upgrade.php b/lib/db/upgrade.php
index 876e190d7ae..53e233d0b9a 100644
--- a/lib/db/upgrade.php
+++ b/lib/db/upgrade.php
@@ -2387,5 +2387,11 @@ function xmldb_main_upgrade($oldversion) {
         upgrade_main_savepoint(true, 2021052500.42);
     }
 
+    if ($oldversion < 2021052500.53) {
+        $DB->delete_records_select('event', "eventtype = 'category' AND categoryid = 0 AND userid <> 0");
+
+        upgrade_main_savepoint(true, 2021052500.53);
+    }
+
     return true;
 }
diff --git a/version.php b/version.php
index b5bb538ccb3..c6427e8fb2b 100644
--- a/version.php
+++ b/version.php
@@ -29,7 +29,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$version  = 2021052500.52;              // YYYYMMDD      = weekly release date of this DEV branch.
+$version  = 2021052500.53;              // YYYYMMDD      = weekly release date of this DEV branch.
                                         //         RR    = release increments - 00 in DEV branches.
                                         //           .XX = incremental changes.
 $release  = '4.0dev (Build: 20210115)'; // Human-friendly version name