diff --git a/job_creator.php b/job_creator.php
index c78e067..c49dc81 100644
--- a/job_creator.php
+++ b/job_creator.php
@@ -368,7 +368,26 @@ private function createPhpunitJobs(
     private function getListOfPhpVersionsByBranchName(): array
     {
         $branch = $this->getInstallerBranch();
-        return MetaData::PHP_VERSIONS_FOR_CMS_RELEASES[$branch] ?? MetaData::PHP_VERSIONS_FOR_CMS_RELEASES['4'];
+        if (isset(MetaData::PHP_VERSIONS_FOR_CMS_RELEASES[$branch])) {
+            return MetaData::PHP_VERSIONS_FOR_CMS_RELEASES[$branch];
+        }
+        // Fallback to using a CMS major based on the version of PHP in composer.json
+        $json = $this->getComposerJsonContent();
+        if ($json) {
+            $php = $json->require->php ?? null;
+            $php = str_replace('^', '', $php);
+            $cmsMajors = array_keys(MetaData::PHP_VERSIONS_FOR_CMS_RELEASES);
+            $cmsMajors = array_filter($cmsMajors, fn($v) => !str_contains($v, '.'));
+            $cmsMajors = array_reverse($cmsMajors);
+            foreach ($cmsMajors as $cmsMajor) {
+                $phpVersions = MetaData::PHP_VERSIONS_FOR_CMS_RELEASES[$cmsMajor];
+                if (in_array($php, $phpVersions)) {
+                    return $phpVersions;
+                }
+            }
+        }
+        // Fallback to the PHP versions allowed for the lowest supported major release line
+        return MetaData::PHP_VERSIONS_FOR_CMS_RELEASES[MetaData::LOWEST_SUPPORTED_CMS_MAJOR];
     }
 
     /**
diff --git a/tests/JobCreatorTest.php b/tests/JobCreatorTest.php
index 2a51cd7..570db2b 100644
--- a/tests/JobCreatorTest.php
+++ b/tests/JobCreatorTest.php
@@ -1988,16 +1988,16 @@ public function provideGetInstallerVersionFromComposer(): array
             // the `6.0` branches are created - currently only `6` branches exist
             ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/framework' => '6.x-dev'], 'silverstripe-module', '6.x-dev'],
             ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/framework' => '6.0.x-dev'], 'silverstripe-vendormodule', '6.0.x-dev'],
-            ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/framework' => '^6'], 'silverstripe-theme', '6.x-dev'],
-            ['myaccount/silverstripe-somemodule', 'mybranch', ['silverstripe/cms' => '^6'], 'silverstripe-recipe', '6.x-dev'],
-            ['myaccount/silverstripe-somemodule', 'mybranch', ['silverstripe/admin' => '^3'], 'silverstripe-vendormodule', '6.x-dev'],
+            ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/framework' => '^6'], 'silverstripe-theme', '6.0.x-dev'],
+            ['myaccount/silverstripe-somemodule', 'mybranch', ['silverstripe/cms' => '^6'], 'silverstripe-recipe', '6.0.x-dev'],
+            ['myaccount/silverstripe-somemodule', 'mybranch', ['silverstripe/admin' => '^3'], 'silverstripe-vendormodule', '6.0.x-dev'],
             ['myaccount/silverstripe-somemodule', '4', ['silverstripe/framework' => '^6'], 'silverstripe-vendormodule', '6.x-dev'],
             ['myaccount/silverstripe-somemodule', '4', ['silverstripe/framework' => '^6'], 'package', ''],
             ['myaccount/silverstripe-somemodule', '4', ['silverstripe/framework' => '^6'], '', ''],
             ['myaccount/silverstripe-somemodule', '4', [], '', ''],
             // // recipe-plugin and vendor-plugin do not override framework
-            ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/recipe-plugin' => '^2', 'silverstripe/framework' => '^6'], 'silverstripe-vendormodule', '6.x-dev'],
-            ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/vendor-plugin' => '^2', 'silverstripe/framework' => '^6'], 'silverstripe-vendormodule', '6.x-dev'],
+            ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/recipe-plugin' => '^2', 'silverstripe/framework' => '^6'], 'silverstripe-vendormodule', '6.0.x-dev'],
+            ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/vendor-plugin' => '^2', 'silverstripe/framework' => '^6'], 'silverstripe-vendormodule', '6.0.x-dev'],
         ];
     }
 
@@ -2299,4 +2299,80 @@ public function testDuplicateJobsRemoved(): void
         ];
         $this->assertSame($expected, $actual);
     }
+
+    public function providePhpFallbackDoorman(): array
+    {
+        return [
+            'php81' => [
+                'php' => '^8.1',
+                'exception' => false,
+                'expected' => [
+                    '8.1 prf-low mariadb phpunit all',
+                    '8.2 mysql80 phpunit all',
+                    '8.3 mysql84 phpunit all',
+                ],
+            ],
+            'php83' => [
+                'php' => '^8.3',
+                'exception' => false,
+                'expected' => [
+                    '8.3 prf-low mariadb phpunit all',
+                    '8.3 mysql80 phpunit all',
+                    '8.4 mysql84 phpunit all',
+                ],
+            ],
+            'none' => [
+                'php' => 'none',
+                'exception' => true,
+                'expected' => null,
+            ],
+        ];
+    }
+
+    /**
+     * @dataProvider providePhpFallbackDoorman
+     */
+    public function testPhpFallbackDoorman(string $php, bool $exception, ?array $expected): void
+    {
+        if (!function_exists('yaml_parse')) {
+            $this->markTestSkipped('yaml extension is not installed');
+        }
+        if ($exception) {
+            $this->expectException(Exception::class);
+        }
+        try {
+            $yml = implode("\n", [
+                <<<EOT
+                composer_install: false
+                endtoend: true
+                js: true
+                phpcoverage: false
+                phpcoverage_force_off: false
+                phplinting: true
+                phpunit: true
+                doclinting: true
+                phpunit_skip_suites: ''
+                dynamic_matrix: true
+                simple_matrix: false
+                github_repository: 'silverstripe/doorman'
+                github_my_ref: '5'
+                parent_branch: ''
+                EOT
+            ]);
+            $creator = new JobCreator();
+            $creator->composerJsonPath = '__composer.json';
+            $this->writeComposerJson(['php' => $php]);
+            $creator->githubRepository = 'silverstripe/doorman';
+            $creator->repoName = 'doorman';
+            $creator->branch = '5';
+            $creator->parseRepositoryMetadata();
+            $json = json_decode($creator->createJson($yml));
+            $actual = array_map(fn($job) => $job->name, $json->include);
+            $this->assertSame($expected, $actual);
+        } finally {
+            if (file_exists('__composer.json')) {
+                unlink('__composer.json');
+            }
+        }
+    }
 }