diff --git a/packages/captp/src/captp.js b/packages/captp/src/captp.js
index 2f68f643ae..91d2b68d9b 100644
--- a/packages/captp/src/captp.js
+++ b/packages/captp/src/captp.js
@@ -410,6 +410,7 @@ export const makeCapTP = (
           epoch,
           questionID,
           target,
+          // @ts-expect-error Type 'unknown' is not assignable to type 'Passable<PassableCap, Error>'.
           method: serialize(harden([null, args])),
         });
         return promise;
@@ -425,6 +426,7 @@ export const makeCapTP = (
           epoch,
           questionID,
           target,
+          // @ts-expect-error Type 'unknown' is not assignable to type 'Passable<PassableCap, Error>'.
           method: serialize(harden([prop, args])),
         });
         return promise;
@@ -493,7 +495,6 @@ export const makeCapTP = (
     }
 
     // If we imported this slot, mark it as one our peer exported.
-    // @ts-expect-error map lacks value type
     return slotToImported.get(recvSlot.add(slot));
   }
 
diff --git a/packages/marshal/src/marshal-stringify.js b/packages/marshal/src/marshal-stringify.js
index c07a0d52f8..e581cdefed 100644
--- a/packages/marshal/src/marshal-stringify.js
+++ b/packages/marshal/src/marshal-stringify.js
@@ -44,7 +44,7 @@ harden(stringify);
 
 /**
  * @param {string} str
- * @returns {Passable}
+ * @returns {unknown}
  */
 const parse = str =>
   unserialize(
diff --git a/packages/marshal/src/marshal.js b/packages/marshal/src/marshal.js
index f49dcc062f..ed4ebc2060 100644
--- a/packages/marshal/src/marshal.js
+++ b/packages/marshal/src/marshal.js
@@ -234,12 +234,12 @@ export const makeMarshal = (
   };
 
   const makeFullRevive = slots => {
-    /** @type {Map<number, RemotableObject | Promise>} */
+    /** @type {Map<number>} */
     const valMap = new Map();
 
     /**
      * @param {{iface?: string, index: number}} slotData
-     * @returns {RemotableObject | Promise}
+     * @returns {PassableCap}
      */
     const decodeSlotCommon = slotData => {
       const { iface = undefined, index, ...rest } = slotData;
@@ -346,7 +346,7 @@ export const makeMarshal = (
     const makeDecodeSlotFromSmallcaps = prefix => {
       /**
        * @param {string} stringEncoding
-       * @param {(e: unknown) => Passable} _decodeRecur
+       * @param {(e: unknown) => PassableCap} _decodeRecur
        * @returns {RemotableObject | Promise}
        */
       return (stringEncoding, _decodeRecur) => {
@@ -404,7 +404,7 @@ export const makeMarshal = (
     // which should be considered fixed once we've completed the switch
     // to smallcaps.
     assertPassable(result);
-    return result;
+    return /** @type {PassableCap} */ (result);
   };
 
   return harden({
diff --git a/packages/marshal/src/types.js b/packages/marshal/src/types.js
index d150190e85..c70818bf34 100644
--- a/packages/marshal/src/types.js
+++ b/packages/marshal/src/types.js
@@ -1,21 +1,23 @@
 // @ts-check
 export {};
 
-/** @import {Passable} from '@endo/pass-style' */
+/** @import {Passable, PassableCap} from '@endo/pass-style' */
 
 /**
  * @template Slot
+ * @template {PassableCap} [Value=any]
  * @callback ConvertValToSlot
- * @param {import("@endo/pass-style").PassableCap} val
+ * @param {Value} val
  * @returns {Slot}
  */
 
 /**
  * @template Slot
+ * @template {PassableCap} [Value=any]
  * @callback ConvertSlotToVal
  * @param {Slot} slot
  * @param {string} [iface]
- * @returns {import("@endo/pass-style").PassableCap}
+ * @returns {Value}
  */
 
 /**
@@ -88,7 +90,7 @@ export {};
 /**
  * @template Slot
  * @callback ToCapData
- * @param {any} val a Passable
+ * @param {Passable} val
  * @returns {CapData<Slot>}
  */
 
diff --git a/packages/marshal/src/types.test-d.ts b/packages/marshal/src/types.test-d.ts
index 47ff6da6c3..a94dcd420b 100644
--- a/packages/marshal/src/types.test-d.ts
+++ b/packages/marshal/src/types.test-d.ts
@@ -1,6 +1,11 @@
 import { expectType, expectNotType } from 'tsd';
 
-import type { PrimitiveStyle } from '@endo/pass-style';
+import {
+  Far,
+  type PrimitiveStyle,
+  type RemotableObject,
+} from '@endo/pass-style';
+import { makeMarshal } from './marshal.js';
 
 expectType<PrimitiveStyle>('string');
 expectType<PrimitiveStyle>('number');
@@ -8,3 +13,21 @@ expectType<PrimitiveStyle>('number');
 expectType<PrimitiveStyle>(1);
 // @ts-expect-error
 expectType<PrimitiveStyle>('str');
+
+type KCap = RemotableObject & { getKref: () => string; iface: () => string };
+const valToSlot = (s: KCap) => s.getKref();
+const slotToVal = (s: string) => null as unknown as KCap;
+const marshal = makeMarshal(valToSlot, slotToVal);
+const cycled = marshal.fromCapData(marshal.toCapData(null as unknown as KCap));
+expectType<unknown>(cycled);
+
+const m = makeMarshal();
+type SlottedRemotable = { getBoardId: () => string };
+const foo = Far('foo');
+const foo1 = Far('foo', { getBoardId: () => 'board1' });
+const foo2 = Far('foo', { getBoardId: () => 'board2' });
+const bar = Far('bar');
+const bar1 = Far('bar', { getBoardId: () => 'board1' });
+m.toCapData(harden({ o: foo1 }));
+m.toCapData(harden({ o: foo2 }));
+m.toCapData(harden({ o: bar1 }));
diff --git a/packages/pass-style/src/internal-types.js b/packages/pass-style/src/internal-types.js
index 68d8c01435..d3796eb0de 100644
--- a/packages/pass-style/src/internal-types.js
+++ b/packages/pass-style/src/internal-types.js
@@ -23,6 +23,6 @@ export {};
  * `assertValid` still needs to be called to determine if it
  * actually is valid.
  * @property {(candidate: any,
- *             passStyleOfRecur: PassStyleOf
+ *             passStyleOfRecur: (val: any) => PassStyle
  *            ) => void} assertValid
  */
diff --git a/packages/pass-style/src/passStyleOf.js b/packages/pass-style/src/passStyleOf.js
index 8bc5141b06..12d8563561 100644
--- a/packages/pass-style/src/passStyleOf.js
+++ b/packages/pass-style/src/passStyleOf.js
@@ -168,12 +168,10 @@ const makePassStyleOf = passStyleHelpers => {
           }
           for (const helper of passStyleHelpers) {
             if (helper.canBeValid(inner)) {
-              // @ts-expect-error XXX
               helper.assertValid(inner, passStyleOfRecur);
               return helper.styleName;
             }
           }
-          // @ts-expect-error XXX
           remotableHelper.assertValid(inner, passStyleOfRecur);
           return 'remotable';
         }
@@ -182,7 +180,6 @@ const makePassStyleOf = passStyleHelpers => {
             Fail`Cannot pass non-frozen objects like ${inner}. Use harden()`;
           typeof inner.then !== 'function' ||
             Fail`Cannot pass non-promise thenables`;
-          // @ts-expect-error XXX
           remotableHelper.assertValid(inner, passStyleOfRecur);
           return 'remotable';
         }