diff --git a/pr-checks/changenotes.ts b/pr-checks/changenotes.ts
index 933d255cd5..d05f4ea892 100755
--- a/pr-checks/changenotes.ts
+++ b/pr-checks/changenotes.ts
@@ -50,6 +50,28 @@ function getChangenotes(): ChangenoteFile[] {
   });
 }
 
+/**
+ * Populates the '[UNRELEASED]' section of CHANGELOG.md with the contents
+ * of the changenotes in {@link CHANGENOTES_DIR} and then deletes those changenotes.
+ * @param contents The contents of CHANGELOG.md
+ * @returns The updated contents of CHANGELOG.md
+ */
+export function transferChangenotesToChangelog(contents: string): string {
+  const changenotes = getChangenotes();
+  const changenoteBodies = changenotes.map((c) => c.content.trim());
+  const changenotePaths = changenotes.map((c) => c.absolutePath);
+
+  const changelog = parseChangelog(contents);
+  addBodyLinesToUnreleasedSection(changelog, changenoteBodies);
+  const updatedChangelog = renderChangelog(changelog);
+
+  for (const p of changenotePaths) {
+    fs.unlinkSync(p);
+  }
+
+  return updatedChangelog;
+}
+
 const entryPoint = process.argv[1];
 if (entryPoint && import.meta.url === pathToFileURL(entryPoint).href) {
   try {
@@ -91,26 +113,13 @@ function usage(): ExitCode {
 
 function assemble(): ExitCode {
   try {
-    const changenotes = getChangenotes();
-    const changenoteBodies = changenotes.map((c) => c.content);
-    const changenotePaths = changenotes.map((c) => c.absolutePath);
-
     withChangelog((contents) => {
-      const changelog = parseChangelog(contents);
-      addBodyLinesToUnreleasedSection(changelog, changenoteBodies);
-      return renderChangelog(changelog);
+      return transferChangenotesToChangelog(contents);
     }, {});
-
-    // Delete changenotes only after successful processing.
-    for (const p of changenotePaths) {
-      fs.unlinkSync(p);
-    }
-
     return ExitCode.Success;
   } catch (e) {
     console.error("Failed to assemble changenotes to 'CHANGELOG.md'", e);
   }
-
   return ExitCode.Failure;
 }
 
diff --git a/pr-checks/update-release-branch.ts b/pr-checks/update-release-branch.ts
index 93e50f7ad2..9d46fd3ecd 100755
--- a/pr-checks/update-release-branch.ts
+++ b/pr-checks/update-release-branch.ts
@@ -23,7 +23,13 @@ import { parseArgs } from "node:util";
 
 import { type ApiClient, getApiClient } from "./api-client";
 import * as changelog from "./changelog";
-import { DryRunOption, REPO_ROOT } from "./config";
+import { transferChangenotesToChangelog } from "./changenotes";
+import {
+  CHANGELOG_FILE,
+  CHANGENOTES_DIR,
+  DryRunOption,
+  REPO_ROOT,
+} from "./config";
 import {
   getCurrentVersion,
   replaceVersionInPackageJson,
@@ -693,11 +699,14 @@ export async function prepareNewBranch(
 
     console.log("Updating changelog");
     changelog.withChangelog(
-      (contents) => changelog.setVersionAndDate(version, contents),
+      (contents) => {
+        const populatedContents = transferChangenotesToChangelog(contents);
+        return changelog.setVersionAndDate(version, populatedContents);
+      },
       { ...options, initChangelog: true },
     );
 
-    runGit(["add", "CHANGELOG.md"], {
+    runGit(["add", CHANGELOG_FILE, CHANGENOTES_DIR], {
       dryRun: options.dryRun,
     });
     runGit(["commit", "-m", `Update changelog for v${version}`], {