diff --git a/consts.php b/consts.php
index 4c226b2..cd252c1 100644
--- a/consts.php
+++ b/consts.php
@@ -27,6 +27,10 @@
         '8.1',
         '8.2',
     ],
+    '5.1' => [
+        '8.1',
+        '8.2',
+    ],
     '5' => [
         '8.1',
         '8.2',
@@ -59,6 +63,17 @@
     'recipe-blog',
 ];
 
+// lockstepped repos that are "three less" e.g. silverstripe/admin 1 is for CMS 4
+const LOCKSTEPPED_REPOS_VERSION_IS_THREE_LESS = [
+    'silverstripe-admin',
+    'silverstripe-asset-admin',
+    'silverstripe-assets',
+    'silverstripe-campaign-admin',
+    'silverstripe-errorpage',
+    'silverstripe-versioned',
+    'silverstripe-versioned-admin',
+];
+
 // Repositories that do not require silverstripe/installer to be explicitly added as a dependency for testing
 const NO_INSTALLER_LOCKSTEPPED_REPOS = [
     // these are/include recipe-cms or recipe-core, so we don't want to composer require installer
diff --git a/job_creator.php b/job_creator.php
index 2620e15..d1e5c6f 100644
--- a/job_creator.php
+++ b/job_creator.php
@@ -56,6 +56,25 @@ public function getInstallerVersion(): string
                 }
             }
         }
+        // has a lockstepped .x-dev requirement in composer.json
+        if (file_exists($this->composerJsonPath)) {
+            $json = json_decode(file_get_contents($this->composerJsonPath));
+            foreach (LOCKSTEPPED_REPOS as $lockedSteppedRepo) {
+                $composerRepo = 'silverstripe/' . str_replace('silverstripe-', '', $lockedSteppedRepo);
+                if (isset($json->require->{$composerRepo})) {
+                    $version = $json->require->{$composerRepo};
+                    if (preg_match('#^([0-9\.]+)\.x\-dev$#', $version, $matches)) {
+                        $versionNumber = $matches[1];
+                        // If the lockstepped dependency is "three less" (e.g. silverstripe/admin is 3 major
+                        // versions behind silverstripe/installer), account for that here.
+                        if (in_array($lockedSteppedRepo, LOCKSTEPPED_REPOS_VERSION_IS_THREE_LESS)) {
+                            $versionNumber += 3;
+                        }
+                        return $versionNumber . '.x-dev';
+                    }
+                }
+            }
+        }
         // fallback to use the next-minor or latest-minor version of installer
         $installerVersions = array_keys(INSTALLER_TO_PHP_VERSIONS);
         $installerVersions = array_filter($installerVersions, fn($version) => substr($version, 0, 1) === $cmsMajor);
diff --git a/tests/JobCreatorTest.php b/tests/JobCreatorTest.php
index e4c4247..d26336d 100644
--- a/tests/JobCreatorTest.php
+++ b/tests/JobCreatorTest.php
@@ -673,11 +673,11 @@ public function provideGetInstallerVersionCMS5FromComposer(): array
             ['myaccount/silverstripe-framework', '5', [], '5.x-dev'],
             ['myaccount/silverstripe-framework', '5.10', [], '5.10.x-dev'],
             // fallback to looking at deps in composer.json, use current minor of installer .x-dev
-            ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/framework' => '5.x-dev'], '5.0.x-dev'],
+            ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/framework' => '5.x-dev'], '5.x-dev'],
             ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/framework' => '5.0.x-dev'], '5.0.x-dev'],
-            ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/framework' => '^5'], '5.0.x-dev'],
-            ['myaccount/silverstripe-somemodule', 'mybranch', ['silverstripe/cms' => '^5'], '5.0.x-dev'],
-            ['myaccount/silverstripe-somemodule', 'mybranch', ['silverstripe/admin' => '^2'], '5.0.x-dev'],
+            ['myaccount/silverstripe-admin', 'mybranch', ['silverstripe/framework' => '^5'], '5.1.x-dev'],
+            ['myaccount/silverstripe-somemodule', 'mybranch', ['silverstripe/cms' => '^5'], '5.1.x-dev'],
+            ['myaccount/silverstripe-somemodule', 'mybranch', ['silverstripe/admin' => '^2'], '5.1.x-dev'],
             ['myaccount/silverstripe-somemodule', '3', ['silverstripe/framework' => '^5'], '5.x-dev'],
         ];
     }