diff --git a/packages/vat-data/test/test-durable-classes.js b/packages/vat-data/test/test-durable-classes.js
index b79d35097f0..17c01d1ebcb 100644
--- a/packages/vat-data/test/test-durable-classes.js
+++ b/packages/vat-data/test/test-durable-classes.js
@@ -33,7 +33,7 @@ test('test defineDurableExoClass', t => {
   const makeUpCounter = defineDurableExoClass(
     upCounterKind,
     UpCounterI,
-    /** @param {number} x */
+    /** @param {number} [x] */
     (x = 0) => ({ x }),
     {
       incr(y = 1) {
@@ -69,7 +69,7 @@ test('test defineDurableExoClassKit', t => {
   const makeCounterKit = defineDurableExoClassKit(
     counterKindHandle,
     { up: UpCounterI, down: DownCounterI },
-    /** @param {number} x */
+    /** @param {number} [x] */
     (x = 0) => ({ x }),
     {
       up: {
@@ -124,7 +124,7 @@ test('finish option', t => {
     UpCounterI,
     /**
      * @param {string} name
-     * @param {number} x
+     * @param {number} [x]
      */
     (name, x = 0) => ({ name, x }),
     {
diff --git a/packages/vat-data/test/test-prepare.js b/packages/vat-data/test/test-prepare.js
index 0ddda5e07a2..87b8d9013a3 100644
--- a/packages/vat-data/test/test-prepare.js
+++ b/packages/vat-data/test/test-prepare.js
@@ -32,7 +32,7 @@ test('test prepareExoClass', t => {
     baggage,
     'UpCounter',
     UpCounterI,
-    /** @param {number} x */
+    /** @param {number} [x] */
     (x = 0) => ({ x }),
     {
       incr(y = 1) {
@@ -66,7 +66,7 @@ test('test prepareExoClassKit', t => {
     baggage,
     'Counter',
     { up: UpCounterI, down: DownCounterI },
-    /** @param {number} x */
+    /** @param {number} [x] */
     (x = 0) => ({ x }),
     {
       up: {
diff --git a/packages/vat-data/test/test-virtual-classes.js b/packages/vat-data/test/test-virtual-classes.js
index 7a0c0e4d84b..245b562fdde 100644
--- a/packages/vat-data/test/test-virtual-classes.js
+++ b/packages/vat-data/test/test-virtual-classes.js
@@ -27,7 +27,7 @@ test('test defineVirtualExoClass', t => {
   const makeUpCounter = defineVirtualExoClass(
     'UpCounter',
     UpCounterI,
-    /** @param {number} x */
+    /** @param {number} [x] */
     (x = 0) => ({ x }),
     {
       incr(y = 1) {
@@ -58,7 +58,7 @@ test('test defineVirtualExoClassKit', t => {
   const makeCounterKit = defineVirtualExoClassKit(
     'Counter',
     { up: UpCounterI, down: DownCounterI },
-    /** @param {number} x */
+    /** @param {number} [x] */
     (x = 0) => ({ x }),
     {
       up: {