diff --git a/README.md b/README.md
index 4666c36..d98f466 100644
--- a/README.md
+++ b/README.md
@@ -42,6 +42,27 @@ jobs:
         github-token: "${{ secrets.GITHUB_TOKEN }}"
 ```
 
+If you want to use this action from a workflow file that doesn't run on the `pull_request` or `pull_request_target` events, use the `pull-request-number` input:
+
+```yaml
+name: Auto approve
+
+on:
+  workflow_dispatch:
+    inputs: pullRequestNumber
+      description: Pull request number to auto-approve
+      required: false
+
+jobs:
+  auto-approve:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: hmarr/auto-approve-action@v2
+      with:
+        github-token: ${{ secrets.GITHUB_TOKEN }}
+        pull-request-number: ${{ github.event.inputs.pullRequestNumber }}
+```
+
 ## Why?
 
 GitHub lets you prevent merges of unapproved pull requests. However, it's occasionally useful to selectively circumvent this restriction - for instance, some people want Dependabot's automated pull requests to not require approval.
diff --git a/action.yml b/action.yml
index 5821a09..92117e0 100644
--- a/action.yml
+++ b/action.yml
@@ -7,6 +7,9 @@ inputs:
   github-token:
     description: 'The GITHUB_TOKEN secret'
     required: true
+  pull-request-number:
+    description: '(optional) The ID of a pull request to auto-approve. By default, this action tries to use the pull_request event payload.'
+    required: false
 runs:
   using: 'node12'
   main: 'dist/index.js'
diff --git a/dist/index.js b/dist/index.js
index 30eab5d..01ae5f8 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -5866,24 +5866,27 @@ exports.approve = void 0;
 const core = __importStar(__nccwpck_require__(186));
 const github = __importStar(__nccwpck_require__(438));
 const request_error_1 = __nccwpck_require__(537);
-function approve(token, context) {
+function approve(token, context, prNumber) {
+    var _a;
     return __awaiter(this, void 0, void 0, function* () {
-        const { pull_request: pr } = context.payload;
-        if (!pr) {
-            core.setFailed("Event payload missing `pull_request` key. Make sure you're " +
-                "triggering this action on the `pull_request` or `pull_request_target` events.");
+        if (!prNumber) {
+            prNumber = (_a = context.payload.pull_request) === null || _a === void 0 ? void 0 : _a.number;
+        }
+        if (!prNumber) {
+            core.setFailed("Event payload missing `pull_request` key, and no `pull-request-number` provided as input." +
+                "Make sure you're triggering this action on the `pull_request` or `pull_request_target` events.");
             return;
         }
         const client = github.getOctokit(token);
-        core.info(`Creating approving review for pull request #${pr.number}`);
+        core.info(`Creating approving review for pull request #${prNumber}`);
         try {
             yield client.pulls.createReview({
                 owner: context.repo.owner,
                 repo: context.repo.repo,
-                pull_number: pr.number,
+                pull_number: prNumber,
                 event: "APPROVE",
             });
-            core.info(`Approved pull request #${pr.number}`);
+            core.info(`Approved pull request #${prNumber}`);
         }
         catch (error) {
             if (error instanceof request_error_1.RequestError) {
@@ -5963,7 +5966,13 @@ const approve_1 = __nccwpck_require__(609);
 function run() {
     return __awaiter(this, void 0, void 0, function* () {
         const token = core.getInput("github-token", { required: true });
-        yield approve_1.approve(token, github.context);
+        const prNumber = parseInt(core.getInput("pull-request-number"), 10);
+        if (!Number.isNaN(prNumber)) {
+            yield approve_1.approve(token, github.context, prNumber);
+        }
+        else {
+            yield approve_1.approve(token, github.context);
+        }
     });
 }
 run();
diff --git a/src/approve.test.ts b/src/approve.test.ts
index c34e5c0..e20e115 100644
--- a/src/approve.test.ts
+++ b/src/approve.test.ts
@@ -23,6 +23,18 @@ test("when a review is successfully created", async () => {
   );
 });
 
+test("when a review is successfully created using pull-request-number", async () => {
+  nock("https://api.github.com")
+    .post("/repos/hmarr/test/pulls/101/reviews")
+    .reply(200, { id: 1 });
+
+  await approve("gh-tok", new Context(), 101);
+
+  expect(core.info).toHaveBeenCalledWith(
+    expect.stringContaining("Approved pull request #101")
+  );
+});
+
 test("without a pull request", async () => {
   await approve("gh-tok", new Context());
 
diff --git a/src/approve.ts b/src/approve.ts
index be91989..bf94340 100644
--- a/src/approve.ts
+++ b/src/approve.ts
@@ -3,27 +3,34 @@ import * as github from "@actions/github";
 import { RequestError } from "@octokit/request-error";
 import { Context } from "@actions/github/lib/context";
 
-export async function approve(token: string, context: Context) {
-  const { pull_request: pr } = context.payload;
-  if (!pr) {
+export async function approve(
+  token: string,
+  context: Context,
+  prNumber?: number
+) {
+  if (!prNumber) {
+    prNumber = context.payload.pull_request?.number;
+  }
+
+  if (!prNumber) {
     core.setFailed(
-      "Event payload missing `pull_request` key. Make sure you're " +
-        "triggering this action on the `pull_request` or `pull_request_target` events."
+      "Event payload missing `pull_request` key, and no `pull-request-number` provided as input." +
+        "Make sure you're triggering this action on the `pull_request` or `pull_request_target` events."
     );
     return;
   }
 
   const client = github.getOctokit(token);
 
-  core.info(`Creating approving review for pull request #${pr.number}`);
+  core.info(`Creating approving review for pull request #${prNumber}`);
   try {
     await client.pulls.createReview({
       owner: context.repo.owner,
       repo: context.repo.repo,
-      pull_number: pr.number,
+      pull_number: prNumber,
       event: "APPROVE",
     });
-    core.info(`Approved pull request #${pr.number}`);
+    core.info(`Approved pull request #${prNumber}`);
   } catch (error) {
     if (error instanceof RequestError) {
       switch (error.status) {
diff --git a/src/main.ts b/src/main.ts
index f66c20b..fec0ac5 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -4,7 +4,12 @@ import { approve } from "./approve";
 
 async function run() {
   const token = core.getInput("github-token", { required: true });
-  await approve(token, github.context);
+  const prNumber: number = parseInt(core.getInput("pull-request-number"), 10);
+  if (!Number.isNaN(prNumber)) {
+    await approve(token, github.context, prNumber);
+  } else {
+    await approve(token, github.context);
+  }
 }
 
 run();