diff --git a/.gitignore b/.gitignore
index 1b2bc847..553c78fe 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,4 +7,4 @@ phpdox.xml
 clover.xml
 example/test-data
 phing-latest.phar
-build/
+build/
\ No newline at end of file
diff --git a/src/ComposerRequireChecker/Cli/CheckCommand.php b/src/ComposerRequireChecker/Cli/CheckCommand.php
index 3cc4255f..41ee9b7b 100644
--- a/src/ComposerRequireChecker/Cli/CheckCommand.php
+++ b/src/ComposerRequireChecker/Cli/CheckCommand.php
@@ -40,12 +40,18 @@ protected function configure()
                 'the composer.json of your package, that should be checked',
                 './composer.json'
             )
-        ->addOption(
+            ->addOption(
                 'ignore-parse-errors',
                 null,
                 InputOption::VALUE_NONE,
                 'this will cause ComposerRequireChecker to ignore errors when files cannot be parsed, otherwise'
                 . ' errors will be thrown'
+            )
+            ->addOption(
+                'register-namespace',
+                null,
+                InputOption::VALUE_IS_ARRAY | InputOption::VALUE_OPTIONAL,
+                'vendor/package:namespace:path as if it was psr4'
             );
     }
 
@@ -64,13 +70,14 @@ protected function execute(InputInterface $input, OutputInterface $output): int
         $options = $this->getCheckOptions($input);
 
         $getPackageSourceFiles = new LocateComposerPackageSourceFiles();
+        $manualRegistered = $this->buildManualList($input, $composerJson);
 
         $sourcesASTs = $this->getASTFromFilesLocator($input);
 
         $definedVendorSymbols = (new LocateDefinedSymbolsFromASTRoots())->__invoke($sourcesASTs(
             (new ComposeGenerators())->__invoke(
                 $getPackageSourceFiles($composerJson),
-                (new LocateComposerPackageDirectDependenciesSourceFiles())->__invoke($composerJson)
+                (new LocateComposerPackageDirectDependenciesSourceFiles())->__invoke($composerJson, $manualRegistered)
             )
         ));
 
@@ -145,4 +152,21 @@ private function getASTFromFilesLocator(InputInterface $input): LocateASTFromFil
         return $sourcesASTs;
     }
 
+    /**
+     * @return array
+     */
+    private function buildManualList(InputInterface $input, $composerJson)
+    {
+        if (!$input->hasOption('register-namespace')) {
+            return [];
+        }
+        $packageDir = dirname($composerJson);
+        $namespaces = [];
+        foreach ($input->getOption('register-namespace') as $option) {
+            if (preg_match('!^([^/:]+(/[^/:]+)+):([^:]+):([^:]+)$!i', $option, $matches)) {
+                $namespaces[$packageDir . '/vendor/' . $matches[1]][$matches[3]] = $matches[4];
+            }
+        }
+        return $namespaces;
+    }
 }
diff --git a/src/ComposerRequireChecker/FileLocator/LocateComposerPackageDirectDependenciesSourceFiles.php b/src/ComposerRequireChecker/FileLocator/LocateComposerPackageDirectDependenciesSourceFiles.php
index dacd871b..7cb8d3f3 100644
--- a/src/ComposerRequireChecker/FileLocator/LocateComposerPackageDirectDependenciesSourceFiles.php
+++ b/src/ComposerRequireChecker/FileLocator/LocateComposerPackageDirectDependenciesSourceFiles.php
@@ -6,7 +6,7 @@
 
 final class LocateComposerPackageDirectDependenciesSourceFiles
 {
-    public function __invoke(string $composerJsonPath): Generator
+    public function __invoke(string $composerJsonPath, array $manual = []): Generator
     {
         $packageDir = dirname($composerJsonPath);
 
@@ -22,7 +22,10 @@ function (string $vendorName) use ($packageDir) {
                 continue;
             }
 
-            yield from (new LocateComposerPackageSourceFiles())->__invoke($vendorDir . '/composer.json');
+            yield from (new LocateComposerPackageSourceFiles())->__invoke(
+                $vendorDir . '/composer.json',
+                $manual[$vendorDir] ?? []
+            );
         }
     }
 }
diff --git a/src/ComposerRequireChecker/FileLocator/LocateComposerPackageSourceFiles.php b/src/ComposerRequireChecker/FileLocator/LocateComposerPackageSourceFiles.php
index 874a54e4..0bdf1c8a 100644
--- a/src/ComposerRequireChecker/FileLocator/LocateComposerPackageSourceFiles.php
+++ b/src/ComposerRequireChecker/FileLocator/LocateComposerPackageSourceFiles.php
@@ -6,7 +6,7 @@
 
 final class LocateComposerPackageSourceFiles
 {
-    public function __invoke(string $composerJsonPath): Generator
+    public function __invoke(string $composerJsonPath, array $manual = []): Generator
     {
         $packageDir = dirname($composerJsonPath);
         $composerData = json_decode(file_get_contents($composerJsonPath), true);
@@ -29,6 +29,10 @@ public function __invoke(string $composerJsonPath): Generator
             $this->getFilePaths($composerData['autoload']['psr-4'] ?? [], $packageDir),
             $blacklist
         );
+        yield from $this->locateFilesInFilesInFilesDefinitions(
+            $this->getFilePaths($manual, $packageDir),
+            $blacklist
+        );
     }
 
     private function getFilePaths(array $sourceDirs, string $packageDir): array
diff --git a/test/ComposerRequireCheckerTest/Cli/CheckCommandGetManualListTest.php b/test/ComposerRequireCheckerTest/Cli/CheckCommandGetManualListTest.php
new file mode 100644
index 00000000..5fdd76d2
--- /dev/null
+++ b/test/ComposerRequireCheckerTest/Cli/CheckCommandGetManualListTest.php
@@ -0,0 +1,62 @@
+<?php
+
+namespace ComposerRequireCheckerTest\Cli;
+
+use ComposerRequireChecker\Cli\CheckCommand;
+use PHPUnit\Framework\TestCase;
+use ReflectionClass;
+use ReflectionMethod;
+use Symfony\Component\Console\Input\InputInterface;
+
+class CheckCommandGetManualListTest extends TestCase
+{
+    /**
+     * @return array
+     */
+    public function provideBuildManualList():array
+    {
+        $method = (new ReflectionClass(CheckCommand::class))->getMethod('buildManualList');
+        $method->setAccessible(true);
+        return [
+            [$this->getInputMockForManualList(), $method, []],
+            [$this->getInputMockForManualList(
+                ['abc', 'nope', 'abc/hi:Abc\\:src', 'abc/def/qoi:Qui\\:src/lib/ext', 'abc/def/:Qui\\:src/lib/ext']),
+                $method,
+                [__DIR__ . '/vendor/abc/def/qoi', __DIR__ . '/vendor/abc/hi']
+            ],
+        ];
+    }
+
+    /**
+     * @param array $return
+     * @return InputInterface
+     */
+    private function getInputMockForManualList(array $return = []):InputInterface
+    {
+        $input = $this->getMockBuilder(InputInterface::class)->getMock();
+        $hasReturn = count($return) > 0;
+        $input->expects($this->once())
+            ->method('hasOption')
+            ->with(/** @scrutinizer ignore-type */'register-namespace')
+            ->willReturn($hasReturn);
+        $input->expects($hasReturn ? $this->once() : $this->never())
+            ->method('getOption')
+            ->with(/** @scrutinizer ignore-type */'register-namespace')
+            ->willReturn($return);
+        return $input;
+    }
+
+    /**
+     * @dataProvider provideBuildManualList
+     * Since the command does so much, there's no reasonable way to supply test data
+     * @test
+     */
+    public function testBuildManualList(InputInterface $input, ReflectionMethod $method, array $expected)
+    {
+        $instance = new CheckCommand();
+        $result = $method->invoke($instance, $input, __FILE__);
+        $this->assertInternalType('array', $result);
+        $this->assertCount(count($expected), $result);
+        $this->assertCount(0, array_diff(array_keys($result), $expected));
+    }
+}
\ No newline at end of file
diff --git a/test/ComposerRequireCheckerTest/Cli/CheckCommandTest.php b/test/ComposerRequireCheckerTest/Cli/CheckCommandTest.php
index c955f5ba..788ae501 100644
--- a/test/ComposerRequireCheckerTest/Cli/CheckCommandTest.php
+++ b/test/ComposerRequireCheckerTest/Cli/CheckCommandTest.php
@@ -3,6 +3,7 @@
 namespace ComposerRequireCheckerTest\Cli;
 
 use ComposerRequireChecker\Cli\Application;
+use InvalidArgumentException;
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Console\Tester\CommandTester;
 
@@ -24,7 +25,7 @@ public function setUp()
 
     public function testExceptionIfComposerJsonNotFound()
     {
-        self::expectException(\InvalidArgumentException::class);
+        self::expectException(InvalidArgumentException::class);
 
         $this->commandTester->execute([
             'composer-json' => 'this-will-not-be-found.json'