diff --git a/.github/workflows/e2e-tests.yml b/.github/workflows/e2e-tests.yml
index 99db5336ea1..dde586c3c03 100644
--- a/.github/workflows/e2e-tests.yml
+++ b/.github/workflows/e2e-tests.yml
@@ -1360,6 +1360,12 @@ jobs:
               echo "$OUTPUT"
               ../bashunit assert contains 'Composer packages changed (test/logger); re-analysing the files depending on them and the files with errors.' "$OUTPUT"
               ../bashunit assert contains 'Result cache restored. 1 file will be reanalysed.' "$OUTPUT"
+          - script: |
+              cd e2e/result-cache-deterministic-order
+              composer install
+              ../../bin/phpstan analyse
+              OUTPUT=$(php assert-sorted.php tmp/resultCache.php 2>&1) || { echo "$OUTPUT"; exit 1; }
+              echo "$OUTPUT"
           - script: |
               cd e2e/result-cache-path-repository
               composer install
diff --git a/e2e/result-cache-deterministic-order/.gitignore b/e2e/result-cache-deterministic-order/.gitignore
new file mode 100644
index 00000000000..de4a392c331
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/.gitignore
@@ -0,0 +1,2 @@
+/vendor
+/composer.lock
diff --git a/e2e/result-cache-deterministic-order/assert-sorted.php b/e2e/result-cache-deterministic-order/assert-sorted.php
new file mode 100644
index 00000000000..289805da0d3
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/assert-sorted.php
@@ -0,0 +1,104 @@
+<?php declare(strict_types = 1);
+
+// Fails if an entry section of the result cache, or the packages of a file, are not sorted.
+
+$path = $argv[1] ?? null;
+if ($path === null || !is_file($path)) {
+	fwrite(STDERR, sprintf("Result cache %s does not exist.\n", $path ?? '<missing argument>'));
+	exit(1);
+}
+
+$handle = fopen($path, 'r');
+if ($handle === false) {
+	fwrite(STDERR, sprintf("Cannot open %s.\n", $path));
+	exit(1);
+}
+
+fgets($handle); // the PHP prefix line that keeps the file inert when included
+
+$unsorted = [];
+$sections = 0;
+$packageLists = [];
+while (($header = fgets($handle)) !== false) {
+	$header = rtrim($header, "\n");
+	if ($header === '') {
+		continue;
+	}
+
+	$parts = explode(' ', $header, 2);
+	if (count($parts) !== 2) {
+		fwrite(STDERR, sprintf("Malformed frame header \"%s\".\n", $header));
+		exit(1);
+	}
+
+	[$name, $size] = $parts;
+	if (!str_ends_with($name, '*')) {
+		// a single value, or (with #) payloads described by the index frame before them
+		if ((int) $size > 0) {
+			fread($handle, (int) $size);
+		}
+
+		continue;
+	}
+
+	$name = substr($name, 0, -1);
+	$keys = [];
+	for ($i = 0; $i < (int) $size; $i++) {
+		[$keyLength, $valueLength] = array_map('intval', explode(' ', rtrim((string) fgets($handle), "\n"), 2));
+		$key = unserialize((string) fread($handle, $keyLength));
+		$value = unserialize((string) fread($handle, $valueLength));
+		$keys[] = $key;
+		if ($name !== 'packageDependencies') {
+			continue;
+		}
+
+		$packageLists[$key] = $value;
+	}
+
+	$sections++;
+	$sorted = $keys;
+	sort($sorted);
+	if ($keys === $sorted) {
+		continue;
+	}
+
+	$unsorted[$name] = $keys;
+}
+
+fclose($handle);
+
+if ($sections === 0) {
+	fwrite(STDERR, "The result cache has no entry sections, so nothing was checked.\n");
+	exit(1);
+}
+
+if ($packageLists === []) {
+	fwrite(STDERR, "The result cache recorded no package dependencies, so nothing was checked.\n");
+	exit(1);
+}
+
+$problems = [];
+foreach ($unsorted as $name => $keys) {
+	$problems[] = sprintf('Section "%s" is not in key order: %s', $name, implode(', ', array_map(static fn (int|string $key): string => basename((string) $key), $keys)));
+}
+
+foreach ($packageLists as $file => $packages) {
+	$sortedPackages = $packages;
+	sort($sortedPackages, SORT_STRING);
+	if ($packages === $sortedPackages) {
+		continue;
+	}
+
+	$problems[] = sprintf('The packages of %s are not in order: %s', basename($file), implode(', ', $packages));
+}
+
+if ($problems !== []) {
+	fwrite(STDERR, implode("\n", $problems) . "\n");
+	exit(1);
+}
+
+echo sprintf(
+	"All %d entry sections of the result cache are in key order, and so are the packages of all %d files that have package dependencies.\n",
+	$sections,
+	count($packageLists),
+);
diff --git a/e2e/result-cache-deterministic-order/composer.json b/e2e/result-cache-deterministic-order/composer.json
new file mode 100644
index 00000000000..529d90d62ce
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/composer.json
@@ -0,0 +1,26 @@
+{
+	"name": "phpstan/result-cache-deterministic-order-e2e",
+	"repositories": [
+		{
+			"type": "path",
+			"url": "./logger",
+			"options": {
+				"symlink": false
+			}
+		},
+		{
+			"type": "path",
+			"url": "./mailer",
+			"options": {
+				"symlink": false
+			}
+		}
+	],
+	"require": {
+		"test/logger": "*",
+		"test/mailer": "*"
+	},
+	"autoload": {
+		"classmap": ["src"]
+	}
+}
diff --git a/e2e/result-cache-deterministic-order/logger/composer.json b/e2e/result-cache-deterministic-order/logger/composer.json
new file mode 100644
index 00000000000..8b33c945f93
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/logger/composer.json
@@ -0,0 +1 @@
+{ "name": "test/logger", "version": "1.0.0", "autoload": { "classmap": ["src"] } }
diff --git a/e2e/result-cache-deterministic-order/logger/src/Logger.php b/e2e/result-cache-deterministic-order/logger/src/Logger.php
new file mode 100644
index 00000000000..fa37b4844fb
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/logger/src/Logger.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace Test\Logger;
+
+class Logger
+{
+
+	public function info(string $message): void
+	{
+	}
+
+}
diff --git a/e2e/result-cache-deterministic-order/mailer/composer.json b/e2e/result-cache-deterministic-order/mailer/composer.json
new file mode 100644
index 00000000000..d4f45ef8847
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/mailer/composer.json
@@ -0,0 +1 @@
+{ "name": "test/mailer", "version": "1.0.0", "autoload": { "classmap": ["src"] } }
diff --git a/e2e/result-cache-deterministic-order/mailer/src/Mailer.php b/e2e/result-cache-deterministic-order/mailer/src/Mailer.php
new file mode 100644
index 00000000000..cadb99517ee
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/mailer/src/Mailer.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace Test\Mailer;
+
+class Mailer
+{
+
+	public function send(string $message): void
+	{
+	}
+
+}
diff --git a/e2e/result-cache-deterministic-order/phpstan.neon b/e2e/result-cache-deterministic-order/phpstan.neon
new file mode 100644
index 00000000000..f797b0985db
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/phpstan.neon
@@ -0,0 +1,10 @@
+parameters:
+	level: 5
+	tmpDir: tmp
+	paths:
+		- src
+	parallel:
+		# two jobs, so the files reach the main process interleaved
+		jobSize: 2
+		maximumNumberOfProcesses: 4
+		minimumNumberOfJobsPerProcess: 1
diff --git a/e2e/result-cache-deterministic-order/src/F1.php b/e2e/result-cache-deterministic-order/src/F1.php
new file mode 100644
index 00000000000..0c7d0e81c77
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/src/F1.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace ResultCacheDeterministicOrderE2E;
+
+use Test\Logger\Logger;
+use Test\Mailer\Mailer;
+
+// without the sort, this file records test/mailer before test/logger
+class F1
+{
+
+	public function __construct(private Logger $logger, private Mailer $mailer)
+	{
+	}
+
+	public function doFoo(): void
+	{
+		$this->logger->info('hello');
+		$this->mailer->send('hello');
+	}
+
+}
diff --git a/e2e/result-cache-deterministic-order/src/F2.php b/e2e/result-cache-deterministic-order/src/F2.php
new file mode 100644
index 00000000000..d9710efa630
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/src/F2.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace ResultCacheDeterministicOrderE2E;
+
+use Test\Logger\Logger;
+use Test\Mailer\Mailer;
+
+// without the sort, this file records test/mailer before test/logger
+class F2
+{
+
+	public function __construct(private Logger $logger, private Mailer $mailer)
+	{
+	}
+
+	public function doFoo(): void
+	{
+		$this->logger->info('hello');
+		$this->mailer->send('hello');
+	}
+
+}
diff --git a/e2e/result-cache-deterministic-order/src/F3.php b/e2e/result-cache-deterministic-order/src/F3.php
new file mode 100644
index 00000000000..be311c5d8c9
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/src/F3.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace ResultCacheDeterministicOrderE2E;
+
+use Test\Logger\Logger;
+use Test\Mailer\Mailer;
+
+// without the sort, this file records test/mailer before test/logger
+class F3
+{
+
+	public function __construct(private Logger $logger, private Mailer $mailer)
+	{
+	}
+
+	public function doFoo(): void
+	{
+		$this->logger->info('hello');
+		$this->mailer->send('hello');
+	}
+
+}
diff --git a/e2e/result-cache-deterministic-order/src/F4.php b/e2e/result-cache-deterministic-order/src/F4.php
new file mode 100644
index 00000000000..9af9528da0d
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/src/F4.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace ResultCacheDeterministicOrderE2E;
+
+use Test\Logger\Logger;
+use Test\Mailer\Mailer;
+
+// without the sort, this file records test/mailer before test/logger
+class F4
+{
+
+	public function __construct(private Logger $logger, private Mailer $mailer)
+	{
+	}
+
+	public function doFoo(): void
+	{
+		$this->logger->info('hello');
+		$this->mailer->send('hello');
+	}
+
+}
diff --git a/e2e/result-cache-deterministic-order/tmp/.gitignore b/e2e/result-cache-deterministic-order/tmp/.gitignore
new file mode 100644
index 00000000000..125e34294bf
--- /dev/null
+++ b/e2e/result-cache-deterministic-order/tmp/.gitignore
@@ -0,0 +1,2 @@
+*
+!.*
diff --git a/src/Analyser/ResultCache/ResultCacheManager.php b/src/Analyser/ResultCache/ResultCacheManager.php
index f43162ea10c..40a3310316a 100644
--- a/src/Analyser/ResultCache/ResultCacheManager.php
+++ b/src/Analyser/ResultCache/ResultCacheManager.php
@@ -2032,6 +2032,11 @@ private function save(
 
 		ksort($exportedNodes);
 		ksort($collectedDataRuleResults);
+		ksort($packageDependencies);
+		foreach ($packageDependencies as $file => $packages) {
+			sort($packages);
+			$packageDependencies[$file] = $packages;
+		}
 
 		// The only point where the StubFilesExtensions may run: the analysis is over, bootstrapFiles
 		// have been executed, so the extensions can rely on them. restore() reads these hashes back