diff --git a/dist/index.js b/dist/index.js
index f9d394d571..c482dfdbeb 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -1308,6 +1308,13 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
         step((generator = generator.apply(thisArg, _arguments || [])).next());
     });
 };
+var __asyncValues = (this && this.__asyncValues) || function (o) {
+    if (!Symbol.asyncIterator) throw new TypeError("Symbol.asyncIterator is not defined.");
+    var m = o[Symbol.asyncIterator], i;
+    return m ? m.call(o) : (o = typeof __values === "function" ? __values(o) : o[Symbol.iterator](), i = {}, verb("next"), verb("throw"), verb("return"), i[Symbol.asyncIterator] = function () { return this; }, i);
+    function verb(n) { i[n] = o[n] && function (v) { return new Promise(function (resolve, reject) { v = o[n](v), settle(resolve, reject, v.done, v.value); }); }; }
+    function settle(resolve, reject, d, v) { Promise.resolve(v).then(function(v) { resolve({ value: v, done: d }); }, reject); }
+};
 var __importDefault = (this && this.__importDefault) || function (mod) {
     return (mod && mod.__esModule) ? mod : { "default": mod };
 };
@@ -1345,6 +1352,7 @@ class GitHubHelper {
     }
     createOrUpdate(inputs, baseRepository, headRepository) {
         return __awaiter(this, void 0, void 0, function* () {
+            var _a, e_1, _b, _c;
             const [headOwner] = headRepository.split('/');
             const headBranch = `${headOwner}:${inputs.branch}`;
             // Try to create the pull request
@@ -1377,8 +1385,37 @@ class GitHubHelper {
             // Update the pull request that exists for this branch and base
             core.info(`Fetching existing pull request`);
             const { data: pulls } = yield this.octokit.rest.pulls.list(Object.assign(Object.assign({}, this.parseRepository(baseRepository)), { state: 'open', head: headBranch, base: inputs.base }));
+            let existingPullNumber = undefined;
+            if ((pulls === null || pulls === void 0 ? void 0 : pulls.length) === 0 || pulls === null || pulls === undefined) {
+                core.error(`Failed to fetch existing pull request details through API - fetching all pull requests to manually check`);
+                try {
+                    for (var _d = true, _e = __asyncValues(this.octokit.paginate.iterator(this.octokit.rest.pulls.list, Object.assign(Object.assign({}, this.parseRepository(baseRepository)), { state: 'open', base: inputs.base }))), _f; _f = yield _e.next(), _a = _f.done, !_a; _d = true) {
+                        _c = _f.value;
+                        _d = false;
+                        const response = _c;
+                        const existingPull = response.data.find(pull => pull.head.label === headBranch);
+                        if (existingPull !== undefined) {
+                            existingPullNumber = existingPull.number;
+                            break;
+                        }
+                    }
+                }
+                catch (e_1_1) { e_1 = { error: e_1_1 }; }
+                finally {
+                    try {
+                        if (!_d && !_a && (_b = _e.return)) yield _b.call(_e);
+                    }
+                    finally { if (e_1) throw e_1.error; }
+                }
+            }
+            else {
+                existingPullNumber = pulls[0].number;
+            }
+            if (existingPullNumber === undefined) {
+                throw new Error(`A pull request already exists for ${headBranch} but couldn't acquire the pull number`);
+            }
             core.info(`Attempting update of pull request`);
-            const { data: pull } = yield this.octokit.rest.pulls.update(Object.assign(Object.assign({}, this.parseRepository(baseRepository)), { pull_number: pulls[0].number, title: inputs.title, body: inputs.body }));
+            const { data: pull } = yield this.octokit.rest.pulls.update(Object.assign(Object.assign({}, this.parseRepository(baseRepository)), { pull_number: existingPullNumber, title: inputs.title, body: inputs.body }));
             core.info(`Updated pull request #${pull.number} (${headBranch} => ${inputs.base})`);
             return {
                 number: pull.number,
diff --git a/src/github-helper.ts b/src/github-helper.ts
index 6d41e06d72..242128c5b7 100644
--- a/src/github-helper.ts
+++ b/src/github-helper.ts
@@ -119,10 +119,39 @@ export class GitHubHelper {
       head: headBranch,
       base: inputs.base
     })
+    let existingPullNumber: number | undefined = undefined
+    if (pulls?.length === 0 || pulls === null || pulls === undefined) {
+      core.error(
+        `Failed to fetch existing pull request details through API - fetching all pull requests to manually check`
+      )
+      for await (const response of this.octokit.paginate.iterator(
+        this.octokit.rest.pulls.list,
+        {
+          ...this.parseRepository(baseRepository),
+          state: 'open',
+          base: inputs.base
+        }
+      )) {
+        const existingPull = response.data.find(
+          pull => pull.head.label === headBranch
+        )
+        if (existingPull !== undefined) {
+          existingPullNumber = existingPull.number
+          break
+        }
+      }
+    } else {
+      existingPullNumber = pulls[0].number
+    }
+    if (existingPullNumber === undefined) {
+      throw new Error(
+        `A pull request already exists for ${headBranch} but couldn't acquire the pull number`
+      )
+    }
     core.info(`Attempting update of pull request`)
     const {data: pull} = await this.octokit.rest.pulls.update({
       ...this.parseRepository(baseRepository),
-      pull_number: pulls[0].number,
+      pull_number: existingPullNumber,
       title: inputs.title,
       body: inputs.body
     })