diff --git a/packages/SwingSet/src/kernel/deviceTranslator.js b/packages/SwingSet/src/kernel/deviceTranslator.js
index 229d27512aaf..6152e4b4943b 100644
--- a/packages/SwingSet/src/kernel/deviceTranslator.js
+++ b/packages/SwingSet/src/kernel/deviceTranslator.js
@@ -69,7 +69,7 @@ function makeDRTranslator(deviceID, kernelKeeper) {
  *
  * @param {string} deviceID
  * @param {string} deviceName
- * @param {*} kernelKeeper
+ * @param {KernelKeeper} kernelKeeper
  * @returns {(dsc: DeviceSyscallObject) => KernelSyscallObject}
  */
 export function makeDSTranslator(deviceID, deviceName, kernelKeeper) {
diff --git a/packages/SwingSet/src/kernel/gc-actions.js b/packages/SwingSet/src/kernel/gc-actions.js
index 01adbeeff45b..eebe81652ac4 100644
--- a/packages/SwingSet/src/kernel/gc-actions.js
+++ b/packages/SwingSet/src/kernel/gc-actions.js
@@ -34,7 +34,7 @@ function parseAction(s) {
 }
 
 /**
- * @param {*} kernelKeeper
+ * @param {KernelKeeper} kernelKeeper
  * @returns {import('../types-internal.js').RunQueueEvent | undefined}
  */
 export function processGCActionSet(kernelKeeper) {
@@ -66,11 +66,18 @@ export function processGCActionSet(kernelKeeper) {
   // whether the current state of the c-lsits and reference counts warrants
   // permits the action to run, or if it should be negated/bypassed.
 
+  /**
+   *
+   * @param {VatKeeper} vatKeeper
+   * @param {unknown} action
+   * @param {string} type
+   * @param {string} kref
+   */
+  // FIXME does nothing with the 'action' argument
   function filterAction(vatKeeper, action, type, kref) {
     const hasCList = vatKeeper.hasCListEntry(kref);
     const isReachable = hasCList ? vatKeeper.getReachableFlag(kref) : undefined;
     const exists = kernelKeeper.kernelObjectExists(kref);
-    // @ts-expect-error xxx
     const { reachable, recognizable } = exists
       ? kernelKeeper.getObjectRefCount(kref)
       : {};
diff --git a/packages/SwingSet/src/kernel/kernel.js b/packages/SwingSet/src/kernel/kernel.js
index 200a69a434b3..2595ef410370 100644
--- a/packages/SwingSet/src/kernel/kernel.js
+++ b/packages/SwingSet/src/kernel/kernel.js
@@ -51,7 +51,7 @@ function abbreviateReplacer(_, arg) {
 /**
  * Provide the kref of a vat's root object, as if it had been exported.
  *
- * @param {*} kernelKeeper  Kernel keeper managing persistent kernel state.
+ * @param {KernelKeeper} kernelKeeper  Kernel keeper managing persistent kernel state.
  * @param {string} vatID  Vat ID of the vat whose root kref is sought.
  *
  * @returns {string} the kref of the root object of the given vat.
diff --git a/packages/SwingSet/src/kernel/state/kernelKeeper.js b/packages/SwingSet/src/kernel/state/kernelKeeper.js
index 192be013c41a..06972d4dd500 100644
--- a/packages/SwingSet/src/kernel/state/kernelKeeper.js
+++ b/packages/SwingSet/src/kernel/state/kernelKeeper.js
@@ -132,6 +132,7 @@ const enableKernelGC = true;
 // Prefix reserved for host written data:
 // host.
 
+/** @type {(s: string) => string[]} s */
 export function commaSplit(s) {
   if (s === '') {
     return [];
@@ -500,7 +501,9 @@ export default function makeKernelKeeper(kernelStorage, kernelSlog) {
 
   function getObjectRefCount(kernelSlot) {
     const data = kvStore.get(`${kernelSlot}.refCount`);
-    data || Fail`getObjectRefCount(${kernelSlot}) was missing`;
+    if (!data) {
+      throw Fail`getObjectRefCount(${kernelSlot}) was missing`;
+    }
     const [reachable, recognizable] = commaSplit(data).map(Number);
     reachable <= recognizable ||
       Fail`refmismatch(get) ${kernelSlot} ${reachable},${recognizable}`;
@@ -1635,3 +1638,4 @@ export default function makeKernelKeeper(kernelStorage, kernelSlog) {
     dump,
   });
 }
+/** @typedef {ReturnType<typeof makeKernelKeeper>} KernelKeeper */
diff --git a/packages/SwingSet/src/types-external.js b/packages/SwingSet/src/types-external.js
index a62c411bd6bd..bdb8039b0e7a 100644
--- a/packages/SwingSet/src/types-external.js
+++ b/packages/SwingSet/src/types-external.js
@@ -124,7 +124,7 @@ export {};
  *
  * @typedef { { transcriptCount: number } } VatStats
  * @typedef { ReturnType<typeof import('./kernel/state/vatKeeper.js').makeVatKeeper> } VatKeeper
- * @typedef { ReturnType<typeof import('./kernel/state/kernelKeeper.js').default> } KernelKeeper
+ * @typedef { import('./kernel/state/kernelKeeper.js').KernelKeeper } KernelKeeper
  * @typedef { Awaited<ReturnType<typeof import('@agoric/xsnap').xsnap>> } XSnap
  * @typedef { (dr: VatDeliveryResult) => void } SlogFinishDelivery
  * @typedef { (ksr: KernelSyscallResult, vsr: VatSyscallResult) => void } SlogFinishSyscall