diff --git a/db/install.xml b/db/install.xml
index 474abd48..9f7d3be1 100644
--- a/db/install.xml
+++ b/db/install.xml
@@ -52,6 +52,7 @@
       </FIELDS>
       <KEYS>
         <KEY NAME="primary" TYPE="primary" FIELDS="id" COMMENT="Primary key for customcert_issues"/>
+        <KEY NAME="user" TYPE="foreign" FIELDS="userid" REFTABLE="user" REFFIELDS="id"/>
         <KEY NAME="customcert" TYPE="foreign" FIELDS="customcertid" REFTABLE="customcert" REFFIELDS="id"/>
       </KEYS>
       <INDEXES>
diff --git a/db/upgrade.php b/db/upgrade.php
index a4a2bc7c..40443cc7 100644
--- a/db/upgrade.php
+++ b/db/upgrade.php
@@ -213,5 +213,14 @@ function xmldb_customcert_upgrade($oldversion) {
         upgrade_mod_savepoint(true, 2022041906, 'customcert'); // Replace with the actual version number.
     }
 
+    if ($oldversion < 2022041908) {
+        $table = new xmldb_table('customcert_issues');
+        $key = new xmldb_key('userid', XMLDB_KEY_FOREIGN, ['userid'], 'user', ['id']);
+
+        $dbman->add_key($table, $key);
+
+        upgrade_mod_savepoint(true, 2022041908, 'customcert');
+    }
+
     return true;
 }
diff --git a/version.php b/version.php
index 2af604de..d52187f0 100644
--- a/version.php
+++ b/version.php
@@ -24,7 +24,7 @@
 
 defined('MOODLE_INTERNAL') || die('Direct access to this script is forbidden.');
 
-$plugin->version   = 2022041906; // The current module version (Date: YYYYMMDDXX).
+$plugin->version   = 2022041908; // The current module version (Date: YYYYMMDDXX).
 $plugin->requires  = 2022041900; // Requires this Moodle version (4.0).
 $plugin->cron      = 0; // Period for cron to check this module (secs).
 $plugin->component = 'mod_customcert';