diff --git a/.husky/post-merge b/.husky/post-merge
new file mode 100755
index 00000000000..a9157b5f60d
--- /dev/null
+++ b/.husky/post-merge
@@ -0,0 +1,15 @@
+#!/bin/sh
+# Generated with husky-init and https://github.com/typicode/husky-4-to-6
+. "$(dirname "$0")/_/husky.sh"
+
+# ATLASSIAN: Update self-published (nightly) versions as part of a merge.
+# Ideally, this would be done as part of a `pre-merge-commit` hook,
+# but git does not support modifying the index during a merge commit.
+# So, we hack it in this `post-merge` hook by immediately ammending the commit.
+# Note that in cases where the merge commit did not automatically succeed,
+# this hook will not be run. See comments in `pre-commit` hook for more.
+yarn update-self-published -a
+if [[ -f .git/MERGE_HEAD ]]; then
+  rm .git/MERGE_HEAD
+fi
+git log -n 1 --pretty=tformat:%s%n%n%b | git commit -F - --amend
diff --git a/.husky/pre-commit b/.husky/pre-commit
index 5ec2f9970aa..3f301f9a53c 100755
--- a/.husky/pre-commit
+++ b/.husky/pre-commit
@@ -3,3 +3,14 @@
 . "$(dirname "$0")/_/husky.sh"
 
 yarn lint-staged
+
+# ATLASSIAN: Update self-published (nightly) versions as part of a merge.
+# If a merge is committed automatically (e.g., no conflicts), this hook
+# will not be run (see comments in `post-merge` for more). However,
+# if a merge is not committed automatically  (e.g., there are conflicts),
+# the `post-merge` hook will not be run. Here we detect that a merge
+# is being manually committed and replicate the work our `post-merge` hook
+# would have done if the merge commit had proceeded automatically.
+if git rev-parse -q --verify MERGE_HEAD >/dev/null 2>&1; then
+  yarn update-self-published -a
+fi
diff --git a/package.json b/package.json
index 7361104e92b..46b176c528e 100644
--- a/package.json
+++ b/package.json
@@ -29,6 +29,7 @@
     "test:integration-ci": "yarn workspace @parcel/integration-tests test-ci",
     "test": "yarn test:unit && yarn test:integration",
     "update-readme-toc": "doctoc README.md",
+    "update-self-published": "node scripts/update-self-published.js",
     "version:atlassian": "yarn lerna version patch --exact --force-publish=@atlassian/internal-parcel-utils,@atlassian/parcel-reporter-analytics",
     "nightly:release": "lerna publish -y --canary --preid nightly --dist-tag=nightly --exact --force-publish=* --no-git-tag-version --no-push",
     "tag:prerelease": "lerna version --exact --force-publish=* --no-git-tag-version --no-push && yarn adjust-versions --exact",
diff --git a/packages/optimizers/image/package.json b/packages/optimizers/image/package.json
index 1dd6de71290..2f5a20523b4 100644
--- a/packages/optimizers/image/package.json
+++ b/packages/optimizers/image/package.json
@@ -37,7 +37,7 @@
     "@parcel/utils": "2.0.24",
     "@parcel/workers": "2.0.24",
     "detect-libc": "^1.0.3",
-    "self-published": "npm:@parcel/optimizer-image@2.5.1-nightly.2696"
+    "self-published": "npm:@parcel/optimizer-image@2.5.1-nightly.2700"
   },
   "devDependencies": {
     "@napi-rs/cli": "^2.6.2",
diff --git a/packages/transformers/js/package.json b/packages/transformers/js/package.json
index 449e43083e9..bb798371bdf 100644
--- a/packages/transformers/js/package.json
+++ b/packages/transformers/js/package.json
@@ -40,7 +40,7 @@
     "detect-libc": "^1.0.3",
     "nullthrows": "^1.1.1",
     "regenerator-runtime": "^0.13.7",
-    "self-published": "npm:@parcel/transformer-js@2.0.0-nightly.1073",
+    "self-published": "npm:@parcel/transformer-js@2.0.0-nightly.1077",
     "semver": "^5.7.1"
   },
   "devDependencies": {
diff --git a/packages/utils/fs-search/package.json b/packages/utils/fs-search/package.json
index 74add031c97..b401d7c8703 100644
--- a/packages/utils/fs-search/package.json
+++ b/packages/utils/fs-search/package.json
@@ -29,7 +29,7 @@
   },
   "dependencies": {
     "detect-libc": "^1.0.3",
-    "self-published": "npm:@parcel/fs-search@2.5.1-nightly.2696"
+    "self-published": "npm:@parcel/fs-search@2.5.1-nightly.2700"
   },
   "devDependencies": {
     "@napi-rs/cli": "^2.6.2"
diff --git a/packages/utils/hash/package.json b/packages/utils/hash/package.json
index 6a7a3708cc9..012381e8af6 100644
--- a/packages/utils/hash/package.json
+++ b/packages/utils/hash/package.json
@@ -33,7 +33,7 @@
   },
   "dependencies": {
     "detect-libc": "^1.0.3",
-    "self-published": "npm:@parcel/hash@2.5.1-nightly.2696",
+    "self-published": "npm:@parcel/hash@2.5.1-nightly.2700",
     "xxhash-wasm": "^0.4.2"
   },
   "devDependencies": {
diff --git a/scripts/update-self-published.js b/scripts/update-self-published.js
new file mode 100755
index 00000000000..4a0cb938388
--- /dev/null
+++ b/scripts/update-self-published.js
@@ -0,0 +1,112 @@
+#!/usr/bin/env node
+
+/* eslint-disable no-console */
+const fs = require('fs');
+const path = require('path');
+const exec = require('child_process').execSync;
+
+const UPSTREAM = /github.+parcel-bundler\/parcel/;
+const NIGHTLY = /.*-nightly\..*/;
+
+if (process.argv.includes('-h') || process.argv.includes('--help')) {
+  console.log(
+    [
+      `  Usage: ${path.basename(process.argv[1])} [opts]`,
+      '',
+      '  Options:',
+      '    -h, --help       Show help',
+      '    -a               Add updated files to git index',
+      '                     (handy in a precommit hook)',
+      '',
+      '  Looks for self-published packages (e.g., @parcel/transformer-js),',
+      '  and compares their nightly version numbers to the list',
+      '  of published nightly versions (via `yarn info`).',
+      '  If it finds a version that is newer, it updates the version',
+      '  in the package.json.',
+      '',
+      '  It will use the oldest nightly version that is newer than',
+      '  the latest common commit between HEAD and the upstream default branch.',
+    ].join('\n'),
+  );
+  process.exit();
+}
+
+const shouldStage = process.argv.includes('-a');
+
+const fromVersionString = str => str.match(/npm:.+@(.+)$/)[1];
+const toVersionString = (name, version) => `npm:${name}@${version}`;
+
+function run(cmd) {
+  let result = exec(cmd, {stdio: [0, 'pipe', 2]});
+  try {
+    return JSON.parse(result);
+  } catch (e) {
+    if (e instanceof SyntaxError) {
+      return result.toString().trim();
+    } else {
+      throw e;
+    }
+  }
+}
+
+function getUpstreamRemoteName() {
+  for (let name of run(`git remote`).split(/\s+/)) {
+    if (UPSTREAM.test(run(`git remote get-url ${name}`))) {
+      return name;
+    }
+  }
+  throw new Error('Could not determine an upstream remote name!');
+}
+
+function getDefaultBranchName(remote) {
+  return run(`git rev-parse --abbrev-ref ${remote}`).split(`${remote}/`).pop();
+}
+
+/**
+ * Check nightly version timestamps for the given `pkgName`
+ * in reverse chronological order, returning the version
+ * with the timestamp closest to `time` without being younger.
+ */
+function getNearestNightlyVersion(pkgName, time) {
+  let candidate = null;
+  let info = run(`yarn info ${pkgName} --json`);
+  let versions = [...Object.entries(info.data.time)].reverse();
+  for (let [version, timestamp] of versions) {
+    if (NIGHTLY.test(version)) {
+      let versionTime = new Date(timestamp);
+      if (versionTime < time) break;
+      candidate = version;
+    }
+  }
+  return candidate;
+}
+
+console.log(`Updating self-published (nightly) versions...`);
+
+let packages = run(
+  `${path.join(__dirname, '..', 'node_modules', '.bin', 'lerna')} ls --json`,
+);
+
+// Fetch the default upstream branch...
+let upstream = getUpstreamRemoteName();
+let branch = getDefaultBranchName(upstream);
+run(`git fetch -q ${upstream} ${branch}`);
+// ...so we can determine the latest common ancestor commit.
+let baseRef = run(`git merge-base HEAD ${upstream}/${branch}`).split(/\s+/)[0];
+// Get the commit time of the latest common ancestor between HEAD and upstream.
+let baseRefTime = new Date(run(`git show -s --format=%cI ${baseRef}`));
+
+for (let {location, name} of packages) {
+  let pkgPath = path.join(location, 'package.json');
+  let pkg = JSON.parse(fs.readFileSync(pkgPath, 'utf8'));
+  if (pkg.dependencies && 'self-published' in pkg.dependencies) {
+    let current = fromVersionString(pkg.dependencies['self-published']);
+    let nightly = getNearestNightlyVersion(name, baseRefTime);
+    if (nightly && current !== nightly) {
+      console.log(`updating ${name} to nearest nightly ${nightly}`);
+      pkg.dependencies['self-published'] = toVersionString(name, nightly);
+      fs.writeFileSync(pkgPath, JSON.stringify(pkg, null, 2) + '\n');
+      if (shouldStage) run(`git add -u ${pkgPath}`);
+    }
+  }
+}