diff --git a/src/lib/utils.ts b/src/lib/utils.ts
index d7f8891..e46d8fe 100644
--- a/src/lib/utils.ts
+++ b/src/lib/utils.ts
@@ -12,6 +12,10 @@ export function getOwn<T extends object, K extends keyof T>(
   return Object.hasOwn(obj, key) ? obj[key] : undefined
 }
 
+export function assert(condition: unknown, message: string): asserts condition {
+  if (!condition) throw new Error(message)
+}
+
 export class ExhaustivenessError extends Error {
   constructor(value: never) {
     super(`Exhaustiveness check failed. ${value} should be impossible`)
@@ -46,6 +50,14 @@ export type VersionIdObject = {
  * @returns versionId string
  */
 export function getVersionId({ coreDiscoveryKey, index }: VersionIdObject) {
+  assert(
+    coreDiscoveryKey.byteLength >= 32,
+    'version ID core discovery key must be have at least 32 bytes'
+  )
+  assert(
+    Number.isSafeInteger(index) && index >= 0,
+    'version ID index must be a non-negative integer'
+  )
   return coreDiscoveryKey.toString('hex') + '/' + index
 }
 
diff --git a/test/lib/utils.test.js b/test/lib/utils.test.js
index 8201cd3..6056f4f 100644
--- a/test/lib/utils.test.js
+++ b/test/lib/utils.test.js
@@ -1,7 +1,11 @@
 // @ts-check
 import assert from 'node:assert/strict'
 import test from 'node:test'
-import { ExhaustivenessError, getOwn } from '../../dist/lib/utils.js'
+import {
+  ExhaustivenessError,
+  getOwn,
+  getVersionId,
+} from '../../dist/lib/utils.js'
 
 test('getOwn', () => {
   class Foo {
@@ -38,3 +42,48 @@ test('ExhaustivenessError', () => {
     }
   })
 })
+
+test('getVersionId', () => {
+  const coreDiscoveryKeyHex =
+    '1f1c774ac1041092c5d8334316919f43fc9e4db48b2074a2d9d7ecf6df7a1181'
+  const valid = {
+    coreDiscoveryKey: Buffer.from(coreDiscoveryKeyHex, 'hex'),
+    index: 123,
+  }
+
+  assert.equal(
+    getVersionId(valid),
+    coreDiscoveryKeyHex + '/' + 123,
+    'serializing version ID'
+  )
+
+  assert.throws(
+    () => getVersionId({ ...valid, index: -1 }),
+    'throws when index is negative'
+  )
+  assert.throws(
+    () => getVersionId({ ...valid, index: 1.2 }),
+    'throws when index is not an integer'
+  )
+  assert.throws(
+    () => getVersionId({ ...valid, index: NaN }),
+    'throws when index is NaN'
+  )
+  assert.throws(
+    () => getVersionId({ ...valid, index: Infinity }),
+    'throws when index is Infinity'
+  )
+
+  assert.throws(
+    () => getVersionId({ ...valid, coreDiscoveryKey: Buffer.alloc(0) }),
+    'throws when core discovery key is empty'
+  )
+  assert.throws(
+    () =>
+      getVersionId({
+        ...valid,
+        coreDiscoveryKey: valid.coreDiscoveryKey.subarray(0, 31),
+      }),
+    'throws when core discovery key is too short'
+  )
+})