diff --git a/maintain.class.php b/maintain.class.php
index b5b6158..523ea37 100644
--- a/maintain.class.php
+++ b/maintain.class.php
@@ -37,9 +37,22 @@ function install($plugin_version, &$errors=array())
   `name` varchar(128) NULL DEFAULT NULL,
   `email` varchar(128) NULL DEFAULT NULL,
   PRIMARY KEY (`id`)
-) ENGINE=MyISAM DEFAULT CHARSET=utf8
+) ENGINE=MyISAM DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci
 ;');
 
+    // --- charset upgrade (utf8 -> utf8mb4) ---
+$result = pwg_query("SHOW TABLE STATUS LIKE '" . $this->table . "';");
+if ($result and $row = pwg_db_fetch_assoc($result)) {
+  if (strpos($row['Collation'], 'utf8mb4') !== 0) {
+    pwg_query("
+      ALTER TABLE `" . $this->table . "`
+      CONVERT TO CHARACTER SET utf8mb4
+      COLLATE utf8mb4_general_ci
+    ;
+    ");
+  }
+}
+
     // configuration
     if (empty($conf['ContactForm']))
     {