diff --git a/Providers/MMFRestrictedCustomersServiceProvider.php b/Providers/MMFRestrictedCustomersServiceProvider.php
index 93bf992..4871235 100644
--- a/Providers/MMFRestrictedCustomersServiceProvider.php
+++ b/Providers/MMFRestrictedCustomersServiceProvider.php
@@ -70,7 +70,13 @@ class MMFRestrictedCustomersServiceProvider extends ServiceProvider {
 				if ( array_key_exists('mailbox_id', $data) ) {
 					$customer->mailbox_id = $data['mailbox_id'];
 				} else {
-					$customer = Customer::find($customer->id);
+					$customer_id = $customer->id;
+					if ( $customer_id == null ) {
+						Log::error('The creation of a Customer with no link to a Mailbox is not allowed, and has been aborted.');
+						// TODO: Error out more gracefully.
+						abort(500, 'The creation of a Customer with no link to a Mailbox is not allowed, and has been aborted.');
+					}
+					$customer = Customer::find($customer_id);
 					if ( $customer == null ) {
 						Log::error('Trying to use a Customer in another Mailbox than the one it is linked to is not allowed, and has been aborted.');
 						// TODO: Error out more gracefully.