diff --git a/packages/SwingSet/src/types-external.js b/packages/SwingSet/src/types-external.js
index ba999553f816..364a1d6041f5 100644
--- a/packages/SwingSet/src/types-external.js
+++ b/packages/SwingSet/src/types-external.js
@@ -224,7 +224,7 @@ export {};
  * @typedef { [tag: 'create-vat', details: PolicyInputDetails  ]} PolicyInputCreateVat
  * @typedef { [tag: 'crank', details: PolicyInputDetails ] } PolicyInputCrankComplete
  * @typedef { [tag: 'crank-failed', details: PolicyInputDetails ]} PolicyInputCrankFailed
- * @typedef { [tag: 'cleanup', details: { cleanups: number }] } PolicyInputCleanup
+ * @typedef { [tag: 'cleanup', details: { cleanups: number, computrons?: number }] } PolicyInputCleanup
  * @typedef { PolicyInputNone | PolicyInputCreateVat | PolicyInputCrankComplete |
  *            PolicyInputCrankFailed | PolicyInputCleanup } PolicyInput
  * @typedef { boolean } PolicyOutput