diff --git a/database/migrations/2018_05_28_085925_create_purchase_orders_table.php b/database/migrations/2018_05_28_085925_create_purchase_orders_table.php
index a96688c3..0ab7bbe2 100644
--- a/database/migrations/2018_05_28_085925_create_purchase_orders_table.php
+++ b/database/migrations/2018_05_28_085925_create_purchase_orders_table.php
@@ -17,7 +17,7 @@ class CreatePurchaseOrdersTable extends Migration
             $table->increments('id');
             $table->string('image_url');
             $table->double('amount');
-            $table->integer('book_id')->unsigned();
+            $table->integer('book_id')->unsigned()->nullable;
             $table->foreign('book_id')->references('id')->on('bookings');
             $table->timestamps();
         });
diff --git a/database/migrations/2018_06_28_011717_rename_booking_foreignkey_in_po_table.php b/database/migrations/2018_06_28_011717_rename_booking_foreignkey_in_po_table.php
index 98e6832d..aa36fdd9 100644
--- a/database/migrations/2018_06_28_011717_rename_booking_foreignkey_in_po_table.php
+++ b/database/migrations/2018_06_28_011717_rename_booking_foreignkey_in_po_table.php
@@ -17,7 +17,7 @@ class RenameBookingForeignkeyInPoTable extends Migration
         {
             $table->dropForeign(['book_id']);
             $table->dropColumn('book_id');
-            $table->integer('booking_id')->unsigned();
+            $table->integer('booking_id')->unsigned()->nullable();
             $table->foreign('booking_id')->references('id')->on('bookings');
         });
     }