diff --git a/lib/db/upgrade.php b/lib/db/upgrade.php
index dd3643fffcf..9cf7394e91b 100644
--- a/lib/db/upgrade.php
+++ b/lib/db/upgrade.php
@@ -2268,5 +2268,30 @@ function xmldb_main_upgrade($oldversion) {
         upgrade_main_savepoint(true, 2018062800.03);
     }
 
+    if ($oldversion < 2018072500.00) {
+        // Find all duplicate top level categories per context.
+        $duplicates = $DB->get_records_sql("SELECT qc1.*
+                                              FROM {question_categories} qc1
+                                              JOIN {question_categories} qc2
+                                                ON qc1.contextid = qc2.contextid AND qc1.id <> qc2.id
+                                             WHERE qc1.parent = 0 AND qc2.parent = 0
+                                          ORDER BY qc1.contextid, qc1.id");
+
+        // For each context, let the first top category to remain as top category and make the rest its children.
+        $currentcontextid = 0;
+        $chosentopid = 0;
+        foreach ($duplicates as $duplicate) {
+            if ($currentcontextid != $duplicate->contextid) {
+                $currentcontextid = $duplicate->contextid;
+                $chosentopid = $duplicate->id;
+            } else {
+                $DB->set_field('question_categories', 'parent', $chosentopid, ['id' => $duplicate->id]);
+            }
+        }
+
+        // Main savepoint reached.
+        upgrade_main_savepoint(true, 2018072500.00);
+    }
+
     return true;
 }
diff --git a/version.php b/version.php
index 94c593137c0..0ec04158ac3 100644
--- a/version.php
+++ b/version.php
@@ -29,7 +29,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$version  = 2018072000.00;              // YYYYMMDD      = weekly release date of this DEV branch.
+$version  = 2018072500.00;              // YYYYMMDD      = weekly release date of this DEV branch.
                                         //         RR    = release increments - 00 in DEV branches.
                                         //           .XX = incremental changes.