diff --git a/upload/admin/model/extension/payment/coingate.php b/upload/admin/model/extension/payment/coingate.php
index 2f0c6e8..10e3872 100644
--- a/upload/admin/model/extension/payment/coingate.php
+++ b/upload/admin/model/extension/payment/coingate.php
@@ -13,10 +13,17 @@ public function install() {
     ");
 
     // Modify the currency table to allow 4-character currency code
-    $this->db->query("
-      ALTER TABLE `" . DB_PREFIX . "currency`
-      MODIFY `code` VARCHAR(4) COLLATE utf8_general_ci NOT NULL;
+    $query = $this->db->query("
+    SELECT character_maximum_length
+    FROM information_schema.columns
+    WHERE table_name = '" . DB_PREFIX . "currency' and column_name = 'code';
     ");
+    if ((int)$query->row['character_maximum_length'] < 4) {
+      $this->db->query("
+        ALTER TABLE `" . DB_PREFIX . "currency`
+        MODIFY `code` VARCHAR(4) COLLATE utf8_general_ci NOT NULL;
+      ");
+    }
 
     $this->load->model('setting/setting');