diff --git a/lib/Subscription.php b/lib/Subscription.php
index 22bfc174a..fcb55a31d 100644
--- a/lib/Subscription.php
+++ b/lib/Subscription.php
@@ -58,6 +58,10 @@ class Subscription extends ApiResource
     const PAYMENT_BEHAVIOR_ERROR_IF_INCOMPLETE = 'error_if_incomplete';
     const PAYMENT_BEHAVIOR_PENDING_IF_INCOMPLETE = 'pending_if_incomplete';
 
+    const PRORATION_BEHAVIOR_ALWAYS_INVOICE = 'always_invoice';
+    const PRORATION_BEHAVIOR_CREATE_PRORATIONS = 'create_prorations';
+    const PRORATION_BEHAVIOR_NONE = 'none';
+
     const STATUS_ACTIVE = 'active';
     const STATUS_CANCELED = 'canceled';
     const STATUS_INCOMPLETE = 'incomplete';