diff --git a/__tests__/poll.test.ts b/__tests__/poll.test.ts
index 4f9a098..f5f6dff 100644
--- a/__tests__/poll.test.ts
+++ b/__tests__/poll.test.ts
@@ -1,8 +1,10 @@
 import {poll} from '../src/poll'
 
 const client = {
-  checks: {
-    listForRef: jest.fn()
+  rest: {
+    checks: {
+      listForRef: jest.fn()
+    }
   }
 }
 
@@ -19,7 +21,7 @@ const run = () =>
   })
 
 test('returns conclusion of completed check', async () => {
-  client.checks.listForRef.mockResolvedValue({
+  client.rest.checks.listForRef.mockResolvedValue({
     data: {
       check_runs: [
         {
@@ -38,7 +40,7 @@ test('returns conclusion of completed check', async () => {
   const result = await run()
 
   expect(result).toBe('success')
-  expect(client.checks.listForRef).toHaveBeenCalledWith({
+  expect(client.rest.checks.listForRef).toHaveBeenCalledWith({
     owner: 'testOrg',
     repo: 'testRepo',
     ref: 'abcd',
@@ -47,7 +49,7 @@ test('returns conclusion of completed check', async () => {
 })
 
 test('polls until check is completed', async () => {
-  client.checks.listForRef
+  client.rest.checks.listForRef
     .mockResolvedValueOnce({
       data: {
         check_runs: [
@@ -83,11 +85,11 @@ test('polls until check is completed', async () => {
   const result = await run()
 
   expect(result).toBe('failure')
-  expect(client.checks.listForRef).toHaveBeenCalledTimes(3)
+  expect(client.rest.checks.listForRef).toHaveBeenCalledTimes(3)
 })
 
 test(`returns 'timed_out' if exceeding deadline`, async () => {
-  client.checks.listForRef.mockResolvedValue({
+  client.rest.checks.listForRef.mockResolvedValue({
     data: {
       check_runs: [
         {
diff --git a/src/main.ts b/src/main.ts
index 72910ca..5fb86ed 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,5 +1,5 @@
 import * as core from '@actions/core'
-import {context, GitHub} from '@actions/github'
+import github, {context} from '@actions/github'
 import {poll} from './poll'
 
 async function run(): Promise<void> {
@@ -7,7 +7,7 @@ async function run(): Promise<void> {
     const token = core.getInput('token', {required: true})
 
     const result = await poll({
-      client: new GitHub(token),
+      client: github.getOctokit(token),
       log: msg => core.info(msg),
 
       checkName: core.getInput('checkName', {required: true}),
@@ -21,7 +21,7 @@ async function run(): Promise<void> {
 
     core.setOutput('conclusion', result)
   } catch (error) {
-    core.setFailed(error.message)
+    core.setFailed(error instanceof Error ? error : JSON.stringify(error))
   }
 }
 
diff --git a/src/poll.ts b/src/poll.ts
index 73b423a..b82dc49 100644
--- a/src/poll.ts
+++ b/src/poll.ts
@@ -1,8 +1,8 @@
-import {GitHub} from '@actions/github'
+import {GitHub} from '@actions/github/lib/utils'
 import {wait} from './wait'
 
 export interface Options {
-  client: GitHub
+  client: InstanceType<typeof GitHub>
   log: (message: string) => void
 
   checkName: string
@@ -32,7 +32,7 @@ export const poll = async (options: Options): Promise<string> => {
     log(
       `Retrieving check runs named ${checkName} on ${owner}/${repo}@${ref}...`
     )
-    const result = await client.checks.listForRef({
+    const result = await client.rest.checks.listForRef({
       // eslint-disable-next-line @typescript-eslint/camelcase
       check_name: checkName,
       owner,
@@ -51,7 +51,8 @@ export const poll = async (options: Options): Promise<string> => {
       log(
         `Found a completed check with id ${completedCheck.id} and conclusion ${completedCheck.conclusion}`
       )
-      return completedCheck.conclusion
+      // conclusion is only `null` if status is not `completed`.
+      return completedCheck.conclusion!
     }
 
     log(