diff --git a/src/Runner/DefaultTestResultCache.php b/src/Runner/DefaultTestResultCache.php
index 906a28f6d5a..62ee5457192 100644
--- a/src/Runner/DefaultTestResultCache.php
+++ b/src/Runner/DefaultTestResultCache.php
@@ -93,6 +93,36 @@ public function __construct(?string $filepath = null)
         $this->cacheFilename = $filepath ?? $_ENV['PHPUNIT_RESULT_CACHE'] ?? self::DEFAULT_RESULT_CACHE_FILENAME;
     }
 
+    public function __serialize(): array
+    {
+        return [
+            'defects' => $this->defects,
+            'times'   => $this->times,
+        ];
+    }
+
+    public function __unserialize(array $data): void
+    {
+        if (isset($data['times'])) {
+            foreach ($data['times'] as $testName => $testTime) {
+                assert(is_string($testName));
+                assert(is_float($testTime));
+                $this->times[$testName] = $testTime;
+            }
+        }
+
+        if (isset($data['defects'])) {
+            foreach ($data['defects'] as $testName => $testResult) {
+                assert(is_string($testName));
+                assert(is_int($testResult));
+
+                if (in_array($testResult, self::ALLOWED_CACHE_TEST_STATUSES, true)) {
+                    $this->defects[$testName] = $testResult;
+                }
+            }
+        }
+    }
+
     /**
      * @throws Exception
      */
@@ -198,10 +228,7 @@ public function clear(): void
 
     public function serialize(): string
     {
-        return serialize([
-            'defects' => $this->defects,
-            'times'   => $this->times,
-        ]);
+        return serialize($this->__serialize());
     }
 
     /**
@@ -209,25 +236,6 @@ public function serialize(): string
      */
     public function unserialize($serialized): void
     {
-        $data = unserialize($serialized);
-
-        if (isset($data['times'])) {
-            foreach ($data['times'] as $testName => $testTime) {
-                assert(is_string($testName));
-                assert(is_float($testTime));
-                $this->times[$testName] = $testTime;
-            }
-        }
-
-        if (isset($data['defects'])) {
-            foreach ($data['defects'] as $testName => $testResult) {
-                assert(is_string($testName));
-                assert(is_int($testResult));
-
-                if (in_array($testResult, self::ALLOWED_CACHE_TEST_STATUSES, true)) {
-                    $this->defects[$testName] = $testResult;
-                }
-            }
-        }
+        $this->__unserialize(unserialize($serialized));
     }
 }
diff --git a/tests/end-to-end/execution-order/cache-result-legacy.phpt b/tests/end-to-end/execution-order/cache-result-legacy.phpt
new file mode 100644
index 00000000000..64e0d9417cb
--- /dev/null
+++ b/tests/end-to-end/execution-order/cache-result-legacy.phpt
@@ -0,0 +1,34 @@
+--SKIPIF--
+<?php if (PHP_VERSION_ID >= 70400) die('skip The new serialization format is tested in cache-result.phpt.'); ?>
+--TEST--
+phpunit --order-by=no-depends,reverse --cache-result --cache-result-file ./tests/_files/MultiDependencyTest.php
+--FILE--
+<?php declare(strict_types=1);
+$target = tempnam(sys_get_temp_dir(), __FILE__);
+
+$arguments = [
+    '--no-configuration',
+    '--ignore-dependencies',   // keep coverage for legacy CLI option
+    '--order-by=reverse',
+    '--cache-result',
+    '--cache-result-file=' . $target,
+    realpath(__DIR__ . '/../execution-order/_files/MultiDependencyTest.php'),
+];
+\array_splice($_SERVER['argv'], 1, count($arguments), $arguments);
+
+require __DIR__ . '/../../bootstrap.php';
+PHPUnit\TextUI\Command::main(false);
+
+print file_get_contents($target);
+
+unlink($target);
+--EXPECTF--
+PHPUnit %s by Sebastian Bergmann and contributors.
+
+.SS..                                                               5 / 5 (100%)
+
+Time: %s, Memory: %s
+
+OK, but incomplete, skipped, or risky tests!
+Tests: 5, Assertions: 3, Skipped: 2.
+C:37:"PHPUnit\Runner\DefaultTestResultCache":%d:{a:2:{s:7:"defects";a:2:{s:29:"MultiDependencyTest::testFour";i:1;s:30:"MultiDependencyTest::testThree";i:1;}s:5:"times";a:5:{s:29:"MultiDependencyTest::testFive";d:%f;s:29:"MultiDependencyTest::testFour";d:%f;s:30:"MultiDependencyTest::testThree";d:%f;s:28:"MultiDependencyTest::testTwo";d:%f;s:28:"MultiDependencyTest::testOne";d:%f;}}}
diff --git a/tests/end-to-end/execution-order/cache-result.phpt b/tests/end-to-end/execution-order/cache-result.phpt
index 5da20cb84bc..e3c772f9e4b 100644
--- a/tests/end-to-end/execution-order/cache-result.phpt
+++ b/tests/end-to-end/execution-order/cache-result.phpt
@@ -1,3 +1,5 @@
+--SKIPIF--
+<?php if (PHP_VERSION_ID < 70400) die('skip The legacy serialization format is tested in cache-result-legacy.phpt.'); ?>
 --TEST--
 phpunit --order-by=no-depends,reverse --cache-result --cache-result-file ./tests/_files/MultiDependencyTest.php
 --FILE--
@@ -29,4 +31,4 @@ Time: %s, Memory: %s
 
 OK, but incomplete, skipped, or risky tests!
 Tests: 5, Assertions: 3, Skipped: 2.
-C:37:"PHPUnit\Runner\DefaultTestResultCache":%d:{a:2:{s:7:"defects";a:2:{s:29:"MultiDependencyTest::testFour";i:1;s:30:"MultiDependencyTest::testThree";i:1;}s:5:"times";a:5:{s:29:"MultiDependencyTest::testFive";d:%f;s:29:"MultiDependencyTest::testFour";d:%f;s:30:"MultiDependencyTest::testThree";d:%f;s:28:"MultiDependencyTest::testTwo";d:%f;s:28:"MultiDependencyTest::testOne";d:%f;}}}
+O:37:"PHPUnit\Runner\DefaultTestResultCache":%d:{s:7:"defects";a:2:{s:29:"MultiDependencyTest::testFour";i:1;s:30:"MultiDependencyTest::testThree";i:1;}s:5:"times";a:5:{s:29:"MultiDependencyTest::testFive";d:%f;s:29:"MultiDependencyTest::testFour";d:%f;s:30:"MultiDependencyTest::testThree";d:%f;s:28:"MultiDependencyTest::testTwo";d:%f;s:28:"MultiDependencyTest::testOne";d:%f;}}
diff --git a/tests/unit/Runner/TestResultCacheTest.php b/tests/unit/Runner/TestResultCacheTest.php
index 2c4cf3d4082..770a27cca29 100644
--- a/tests/unit/Runner/TestResultCacheTest.php
+++ b/tests/unit/Runner/TestResultCacheTest.php
@@ -43,12 +43,16 @@ public function testDoesClearCacheBeforeLoad(): void
 
     public function testShouldNotSerializePassedTestsAsDefectButTimeIsStored(): void
     {
+        $expectedSerializedData = PHP_VERSION_ID >= 70400
+            ? 'O:37:"PHPUnit\Runner\DefaultTestResultCache":2:{s:7:"defects";a:0:{}s:5:"times";a:1:{s:7:"testOne";d:123;}}'
+            : 'C:37:"PHPUnit\Runner\DefaultTestResultCache":64:{a:2:{s:7:"defects";a:0:{}s:5:"times";a:1:{s:7:"testOne";d:123;}}}';
+
         $cache = new DefaultTestResultCache;
         $cache->setState('testOne', BaseTestRunner::STATUS_PASSED);
         $cache->setTime('testOne', 123);
 
         $data = \serialize($cache);
-        $this->assertSame('C:37:"PHPUnit\Runner\DefaultTestResultCache":64:{a:2:{s:7:"defects";a:0:{}s:5:"times";a:1:{s:7:"testOne";d:123;}}}', $data);
+        $this->assertSame($expectedSerializedData, $data);
     }
 
     public function testCanPersistCacheToFile(): void
@@ -89,8 +93,18 @@ public function testShouldReturnEmptyCacheFromInvalidFile(): void
         $this->assertTrue($this->isSerializedEmptyCache(\serialize($cache)));
     }
 
+    public function testUnserializeFromLegacyFormat(): void
+    {
+        $cache = \unserialize('C:37:"PHPUnit\Runner\DefaultTestResultCache":44:{a:2:{s:7:"defects";a:0:{}s:5:"times";a:0:{}}}');
+
+        $this->assertInstanceOf(DefaultTestResultCache::class, $cache);
+        $this->assertTrue($this->isSerializedEmptyCache(\serialize($cache)));
+    }
+
     public function isSerializedEmptyCache(string $data): bool
     {
-        return $data === 'C:37:"PHPUnit\Runner\DefaultTestResultCache":44:{a:2:{s:7:"defects";a:0:{}s:5:"times";a:0:{}}}';
+        return PHP_VERSION_ID >= 70400
+            ? $data === 'O:37:"PHPUnit\Runner\DefaultTestResultCache":2:{s:7:"defects";a:0:{}s:5:"times";a:0:{}}'
+            : $data === 'C:37:"PHPUnit\Runner\DefaultTestResultCache":44:{a:2:{s:7:"defects";a:0:{}s:5:"times";a:0:{}}}';
     }
 }