diff --git a/lib/AbstractException.php b/lib/AbstractException.php
index cde92dc..5be1008 100644
--- a/lib/AbstractException.php
+++ b/lib/AbstractException.php
@@ -38,6 +38,7 @@ abstract class AbstractException extends \Exception {
         "Db/Exception.updateFileUnreadable"           => 10216,
         "Db/Exception.updateFileError"                => 10217,
         "Db/Exception.updateFileIncomplete"           => 10218,
+        "Db/Exception.updateSchemaChange"             => 10219,
         "Db/Exception.paramTypeInvalid"               => 10221,
         "Db/Exception.paramTypeUnknown"               => 10222,
         "Db/Exception.paramTypeMissing"               => 10223,
diff --git a/lib/Database.php b/lib/Database.php
index 2049f27..19b163d 100644
--- a/lib/Database.php
+++ b/lib/Database.php
@@ -25,7 +25,7 @@ use JKingWeb\Arsse\Rule\Exception as RuleException;
  *
  * - Users
  * - Subscriptions to feeds, which belong to users
- * - Folders, which belong to users and contain subscriptions
+ * - Folders, which belong to users and contain subscriptions or other folders
  * - Tags, which belong to users and can be assigned to multiple subscriptions
  * - Icons, which are associated with subscriptions
  * - Articles, which belong to subscriptions
@@ -76,9 +76,15 @@ class Database {
     public function __construct($initialize = true) {
         $driver = Arsse::$conf->dbDriver;
         $this->db = $driver::create();
+        $this->checkSchemaVersion($initialize);
+    }
+
+    public function checkSchemaVersion(bool $initialize = false): void {
         $ver = $this->db->schemaVersion();
         if ($initialize && $ver < self::SCHEMA_VERSION) {
             $this->db->schemaUpdate(self::SCHEMA_VERSION);
+        } elseif ($ver != self::SCHEMA_VERSION) {
+            throw new Db\Exception("updateSchemaChange");
         }
     }
 
diff --git a/lib/Service.php b/lib/Service.php
index 79a5346..0bbbdd1 100644
--- a/lib/Service.php
+++ b/lib/Service.php
@@ -66,6 +66,7 @@ class Service {
     }
 
     public function checkIn(): bool {
+        Arsse::$db->checkSchemaVersion();
         return Arsse::$db->metaSet("service_last_checkin", time(), "datetime");
     }
 
diff --git a/locale/en.php b/locale/en.php
index c954647..b6b37bb 100644
--- a/locale/en.php
+++ b/locale/en.php
@@ -147,6 +147,7 @@ return [
             0 {Automatic updating of the {driver_name} database failed because it is already up to date with the requested version, {target}}
             other {Automatic updating of the {driver_name} database failed because its version, {current}, is newer than the requested version, {target}}
         }',
+    'Exception.JKingWeb/Arsse/Db/Exception.updateSchemaChange'             => 'Database schema version has changed since the application was started; application restart is required',
     'Exception.JKingWeb/Arsse/Db/Exception.engineErrorGeneral'             => '{0}',
     // indicates programming error
     'Exception.JKingWeb/Arsse/Db/Exception.savepointStatusUnknown'         => 'Savepoint status code {0} not implemented',