diff --git a/.github/workflows/assign_reviewers.yml b/.github/workflows/assign_reviewers.yml
index d4ae7daa6..2395a085d 100644
--- a/.github/workflows/assign_reviewers.yml
+++ b/.github/workflows/assign_reviewers.yml
@@ -1,19 +1,41 @@
 name: Assign requested reviewers
 
+# This workflow adds requested reviewers as assignees. If you remove a
+# requested reviewer, it will not remove them as an assignee.
+#
+# See https://github.com/google/blockly/issues/5643 for more
+# information on why this was added.
+#
+# N.B.: Runs with a read-write repo token.  Do not check out the
+# submitted branch!
 on:
-  pull_request:
+  pull_request_target:
     types: [review_requested]
 
 jobs:
   requested-reviewer:
     runs-on: ubuntu-latest
     steps:
-    - name: Check Out Blockly
-      uses: actions/checkout@v2
-
     - name: Assign requested reviewer
       uses: actions/github-script@v5
       with:
         script: |
-          const {assign} = require('./.github/workflows/scripts/assign_reviewers.js')
-          assign(github, context, core)
+          try {
+            if (context.payload.pull_request === undefined) {
+            throw new Error("Can't get pull_request payload. " +
+                            'Check a request reviewer event was triggered.');
+            }
+            const reviewers = context.payload.pull_request.requested_reviewers;
+            // Assignees takes in a list of logins rather than the
+            // reviewer object.
+            const reviewerNames = reviewers.map(reviewer => reviewer.login);
+            const {number:issue_number} = context.payload.pull_request;
+            github.rest.issues.addAssignees({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: issue_number,
+              assignees: reviewerNames
+            });
+          } catch (error) {
+            core.setFailed(error.message);
+          }
diff --git a/.github/workflows/scripts/assign_reviewers.js b/.github/workflows/scripts/assign_reviewers.js
deleted file mode 100644
index be9980660..000000000
--- a/.github/workflows/scripts/assign_reviewers.js
+++ /dev/null
@@ -1,27 +0,0 @@
-/**
- * This script adds requested reviewers as assignees. If you remove a requested
- * reviewer, it will not remove them as an assignee.
- *
- * See https://github.com/google/blockly/issues/5643 for more information on
- * why this was added.
- */
-exports.assign = function(github, context, core) {
-  try {
-    if (context.payload.pull_request === undefined) {
-      throw new Error("Can't get pull_request payload. Check a request reviewer event was triggered.");
-    }
-    const reviewers = context.payload.pull_request.requested_reviewers;
-    // Assignees takes in a list of logins rather than the reviewer object.
-    const reviewerNames = reviewers.map(reviewer => reviewer.login);
-    const {number:issue_number} = context.payload.pull_request;
-
-    github.rest.issues.addAssignees({
-      owner: context.repo.owner,
-      repo: context.repo.repo,
-      issue_number: issue_number,
-      assignees: reviewerNames
-    });
-  } catch (error) {
-    core.setFailed(error.message);
-  }
-}