diff --git a/docs/app-engine-architecture.md b/docs/app-engine-architecture.md
index d9693af6e..9adf4546e 100644
--- a/docs/app-engine-architecture.md
+++ b/docs/app-engine-architecture.md
@@ -366,10 +366,11 @@ registry codebase:
 *   `Registrar` -- These hold information about client registrars.
 *   `RegistrarContact` -- Registrars have contacts just as domains do. These are
     stored in a special RegistrarContact entity.
-*   `RegistrarCredit` and `RegistrarCreditBalance` -- The system supports the
-    concept of a registrar credit balance, which is a pool of credit that the
-    registrar can use to offset amounts they owe. This might come from
-    promotions, for instance. These entities maintain registrars' balances.
+*   `RegistrarCredit` and `RegistrarCreditBalance` -- These entities implement
+    the concept of registrar "credits" which are pools of credit that would
+    apply to charges owed by the registrar. Note, however, that Nomulus
+    currently has no support for actually incorporating credits into billing
+    output, and these entities may be removed at any time.
 *   `Registry` -- These hold information about the TLDs supported by the
     Registry system.
 *   `RegistryCursor` -- These entities are the predecessor to the Cursor