diff --git a/Readme.rst b/Readme.rst
index cf19a83..6a90ec5 100644
--- a/Readme.rst
+++ b/Readme.rst
@@ -176,3 +176,19 @@ Example:
 .. code:: bash
 
     --runtime-set vendor YourVendor
+
+``mappingFile``
+    Configure where the `LegacyClassnames.php` is located, through ``ruleset.xml`` or using
+    ``--runtime-set``. Default is `LegacyClassnames.php` in the project root.
+
+    Example:
+
+.. code:: xml
+
+    <config name="mappingFile" value="/projects/typo3_installation/vendor/composer/autoload_classaliasmap.php"/>
+
+Example:
+
+.. code:: bash
+
+    --runtime-set mappingFile /projects/typo3_installation/vendor/composer/autoload_classaliasmap.php
diff --git a/src/Standards/Typo3Update/Sniffs/LegacyClassnames/AbstractClassnameChecker.php b/src/Standards/Typo3Update/Sniffs/LegacyClassnames/AbstractClassnameChecker.php
index b72e1d2..218ccee 100644
--- a/src/Standards/Typo3Update/Sniffs/LegacyClassnames/AbstractClassnameChecker.php
+++ b/src/Standards/Typo3Update/Sniffs/LegacyClassnames/AbstractClassnameChecker.php
@@ -20,6 +20,7 @@ namespace Typo3Update\Sniffs\LegacyClassnames;
  * 02110-1301, USA.
  */
 
+use PHP_CodeSniffer as PhpCs;
 use PHP_CodeSniffer_File as PhpCsFile;
 use PHP_CodeSniffer_Sniff as PhpCsSniff;
 use Typo3Update\Sniffs\LegacyClassnames\Mapping;
diff --git a/src/Standards/Typo3Update/Sniffs/LegacyClassnames/Mapping.php b/src/Standards/Typo3Update/Sniffs/LegacyClassnames/Mapping.php
index 885ecfd..e704584 100644
--- a/src/Standards/Typo3Update/Sniffs/LegacyClassnames/Mapping.php
+++ b/src/Standards/Typo3Update/Sniffs/LegacyClassnames/Mapping.php
@@ -50,8 +50,7 @@ class Mapping
     }
     private function __construct()
     {
-        // $mappingFile = $this->getMappingFile();
-        $mappingFile = __DIR__ . '/../../../../../LegacyClassnames.php';
+        $mappingFile = $this->getMappingFile();
 
         $this->mappings = require $mappingFile;
     }
@@ -113,8 +112,7 @@ class Mapping
             return;
         }
 
-        // $mappingFile = $this->getMappingFile();
-        $mappingFile = __DIR__ . '/../../../../../LegacyClassnames.php';
+        $mappingFile = $this->getMappingFile();
 
         file_put_contents(
             $mappingFile,
diff --git a/src/Standards/Typo3Update/Sniffs/OptionsAccessTrait.php b/src/Standards/Typo3Update/Sniffs/OptionsAccessTrait.php
index 3037bd8..7193e07 100644
--- a/src/Standards/Typo3Update/Sniffs/OptionsAccessTrait.php
+++ b/src/Standards/Typo3Update/Sniffs/OptionsAccessTrait.php
@@ -40,4 +40,18 @@ trait OptionsAccessTrait
         }
         return trim($vendor, '\\/');
     }
+
+    /**
+     * Returns the configured file path containing the mappings for classes, interfaced and traits.
+     *
+     * @return string
+     */
+    public function getMappingFile()
+    {
+        $mappingFile = PhpCs::getConfigData('mappingFile');
+        if (!$mappingFile) {
+            $mappingFile = __DIR__ . '/../../../../LegacyClassnames.php';
+        }
+        return $mappingFile;
+    }
 }