diff --git a/framework/db/cubrid/QueryBuilder.php b/framework/db/cubrid/QueryBuilder.php
index bbd688c883..7ea7dc3cff 100644
--- a/framework/db/cubrid/QueryBuilder.php
+++ b/framework/db/cubrid/QueryBuilder.php
@@ -119,6 +119,23 @@ class QueryBuilder extends \yii\db\QueryBuilder
         return 'SELECT CASE WHEN EXISTS(' . $rawSql . ') THEN 1 ELSE 0 END';
     }
 
+    /**
+     * @inheritDoc
+     * @see http://www.cubrid.org/manual/93/en/sql/schema/table.html#drop-index-clause
+     */
+    public function dropIndex($name, $table)
+    {
+        /** @var Schema $schema */
+        $schema = $this->db->getSchema();
+        foreach ($schema->getTableUniques($table) as $unique) {
+            if ($unique->name === $name) {
+                return $this->dropUnique($name, $table);
+            }
+        }
+
+        return 'DROP INDEX ' . $this->db->quoteTableName($name) . ' ON ' . $this->db->quoteTableName($table);
+    }
+
     /**
      * @inheritDoc
      * @throws NotSupportedException this is not supported by CUBRID.
diff --git a/framework/db/mysql/QueryBuilder.php b/framework/db/mysql/QueryBuilder.php
index 41b024ba44..8452383c31 100644
--- a/framework/db/mysql/QueryBuilder.php
+++ b/framework/db/mysql/QueryBuilder.php
@@ -120,6 +120,14 @@ class QueryBuilder extends \yii\db\QueryBuilder
         return 'ALTER TABLE ' . $this->db->quoteTableName($table) . ' DROP PRIMARY KEY';
     }
 
+    /**
+     * @inheritDoc
+     */
+    public function dropUnique($name, $table)
+    {
+        return $this->dropIndex($name, $table);
+    }
+
     /**
      * @inheritDoc
      * @throws NotSupportedException this is not supported by MySQL.