diff --git a/database/migrations/2018_03_18_071831_create_mpesa_bulk_payment_requests_table.php b/database/migrations/2018_03_18_071831_create_mpesa_bulk_payment_requests_table.php
index ec1cadf..e4aa128 100644
--- a/database/migrations/2018_03_18_071831_create_mpesa_bulk_payment_requests_table.php
+++ b/database/migrations/2018_03_18_071831_create_mpesa_bulk_payment_requests_table.php
@@ -15,7 +15,7 @@ public function up()
     {
         Schema::create('mpesa_bulk_payment_requests', function (Blueprint $table) {
             $table->increments('id');
-            $table->string('conversation_id')->index();
+            $table->unique('conversation_id');
             $table->string('originator_conversation_id');
             $table->decimal('amount', 10, 2);
             $table->string('phone', 20);