diff --git a/system/Debug/Exceptions.php b/system/Debug/Exceptions.php
index ef7c45a3ed6e..7f7ca2cb2628 100644
--- a/system/Debug/Exceptions.php
+++ b/system/Debug/Exceptions.php
@@ -372,17 +372,20 @@ protected function determineCodes(Throwable $exception): array
 	 */
 	public static function cleanPath(string $file): string
 	{
-		if (strpos($file, APPPATH) === 0)
+		switch (true)
 		{
-			$file = 'APPPATH/' . substr($file, strlen(APPPATH));
-		}
-		elseif (strpos($file, SYSTEMPATH) === 0)
-		{
-			$file = 'SYSTEMPATH/' . substr($file, strlen(SYSTEMPATH));
-		}
-		elseif (strpos($file, FCPATH) === 0)
-		{
-			$file = 'FCPATH/' . substr($file, strlen(FCPATH));
+			case strpos($file, APPPATH) === 0:
+				$file = 'APPPATH' . DIRECTORY_SEPARATOR . substr($file, strlen(APPPATH));
+				break;
+			case strpos($file, SYSTEMPATH) === 0:
+				$file = 'SYSTEMPATH' . DIRECTORY_SEPARATOR . substr($file, strlen(SYSTEMPATH));
+				break;
+			case strpos($file, FCPATH) === 0:
+				$file = 'FCPATH' . DIRECTORY_SEPARATOR . substr($file, strlen(FCPATH));
+				break;
+			case defined('VENDORPATH') && strpos($file, VENDORPATH) === 0;
+				$file = 'VENDORPATH' . DIRECTORY_SEPARATOR . substr($file, strlen(VENDORPATH));
+				break;
 		}
 
 		return $file;
diff --git a/system/Test/bootstrap.php b/system/Test/bootstrap.php
index 4a217fef12e7..83585f374171 100644
--- a/system/Test/bootstrap.php
+++ b/system/Test/bootstrap.php
@@ -22,6 +22,7 @@
 defined('TESTPATH')      || define('TESTPATH', realpath(HOMEPATH . 'tests/') . DIRECTORY_SEPARATOR);
 defined('SUPPORTPATH')   || define('SUPPORTPATH', realpath(TESTPATH . '_support/') . DIRECTORY_SEPARATOR);
 defined('COMPOSER_PATH') || define('COMPOSER_PATH', realpath(HOMEPATH . 'vendor/autoload.php'));
+defined('VENDORPATH')    || define('VENDORPATH', realpath(HOMEPATH . 'vendor') . DIRECTORY_SEPARATOR);
 
 // Load Common.php from App then System
 if (file_exists(APPPATH . 'Common.php'))
diff --git a/system/bootstrap.php b/system/bootstrap.php
index 33ab45598d07..e014ad05e144 100644
--- a/system/bootstrap.php
+++ b/system/bootstrap.php
@@ -139,6 +139,16 @@ class_alias('Config\Services', 'CodeIgniter\Services');
 // Now load Composer's if it's available
 if (is_file(COMPOSER_PATH))
 {
+	/**
+	 * The path to the vendor directory.
+	 *
+	 * We do not want to enforce this, so set the constant if Composer was used.
+	 */
+	if (! defined('VENDORPATH'))
+	{
+		define('VENDORPATH', realpath(ROOTPATH . 'vendor') . DIRECTORY_SEPARATOR);
+	}
+
 	require_once COMPOSER_PATH;
 }
 
diff --git a/tests/system/Debug/ExceptionsTest.php b/tests/system/Debug/ExceptionsTest.php
index d9f1dae8b8cc..25fdf8890cb3 100644
--- a/tests/system/Debug/ExceptionsTest.php
+++ b/tests/system/Debug/ExceptionsTest.php
@@ -7,4 +7,36 @@ public function testNew()
 		$actual = new Exceptions(new \Config\Exceptions(), \Config\Services::request(), \Config\Services::response());
 		$this->assertInstanceOf(Exceptions::class, $actual);
 	}
+
+	/**
+	 * @dataProvider dirtyPathsProvider
+	 */
+	public function testCleanPaths($file, $expected)
+	{
+		$this->assertEquals($expected, Exceptions::cleanPath($file));
+	}
+
+	public function dirtyPathsProvider()
+	{
+		$ds = DIRECTORY_SEPARATOR;
+
+		return [
+			[
+				APPPATH . 'Config' . $ds . 'App.php',
+				'APPPATH' . $ds . 'Config' . $ds . 'App.php',
+			],
+			[
+				SYSTEMPATH . 'CodeIgniter.php',
+				'SYSTEMPATH' . $ds . 'CodeIgniter.php',
+			],
+			[
+				VENDORPATH . 'autoload.php',
+				'VENDORPATH' . $ds . 'autoload.php',
+			],
+			[
+				FCPATH . 'index.php',
+				'FCPATH' . $ds . 'index.php',
+			],
+		];
+	}
 }