diff --git a/src/Caching/FileHashComputer.php b/src/Caching/FileHashComputer.php
index 559037b3f9..0b5c263f51 100644
--- a/src/Caching/FileHashComputer.php
+++ b/src/Caching/FileHashComputer.php
@@ -5,6 +5,7 @@
 namespace Symplify\EasyCodingStandard\Caching;
 
 use Nette\Utils\Json;
+use ReflectionClass;
 use Symplify\EasyCodingStandard\Application\Version\StaticVersionResolver;
 use Symplify\EasyCodingStandard\Config\ECSConfig;
 use Symplify\EasyCodingStandard\DependencyInjection\SimpleParameterProvider;
@@ -24,8 +25,11 @@ public function computeConfig(string $filePath): string
         $ecsConfig = new ECSConfig();
         $callable($ecsConfig);
 
-        // hash the registered checkers and their configuration
-        $fileHash = sha1(Json::encode($ecsConfig->getCheckerConfiguration()));
+        // hash the registered checkers, their configuration and the source of the local ones
+        $checkerConfiguration = $ecsConfig->getCheckerConfiguration();
+        $fileHash = sha1(
+            Json::encode($checkerConfiguration) . $this->hashLocalCheckerFiles(array_keys($checkerConfiguration))
+        );
 
         return sha1($fileHash . SimpleParameterProvider::hash() . StaticVersionResolver::PACKAGE_VERSION);
     }
@@ -39,4 +43,49 @@ public function compute(string $filePath): string
 
         return $fileHash;
     }
+
+    /**
+     * A checker installed in vendor/ only changes with its package, but a project's own checker can change while its
+     * class name and configuration stay the same, so its code has to be part of the hash.
+     *
+     * @param array<class-string> $checkerClasses
+     */
+    private function hashLocalCheckerFiles(array $checkerClasses): string
+    {
+        $fileHashes = [];
+        foreach ($checkerClasses as $checkerClass) {
+            foreach ($this->resolveClassFileNames(new ReflectionClass($checkerClass)) as $fileName) {
+                if (str_contains($fileName, DIRECTORY_SEPARATOR . 'vendor' . DIRECTORY_SEPARATOR)) {
+                    continue;
+                }
+
+                $fileHashes[$fileName] = $this->compute($fileName);
+            }
+        }
+
+        // contents only, so that the same project checked out elsewhere keeps its cache
+        $fileHashes = array_values($fileHashes);
+        sort($fileHashes);
+
+        return sha1(implode('', $fileHashes));
+    }
+
+    /**
+     * @param ReflectionClass<object> $reflectionClass
+     * @return string[]
+     */
+    private function resolveClassFileNames(ReflectionClass $reflectionClass): array
+    {
+        $fileNames = [];
+        do {
+            $fileNames[] = $reflectionClass->getFileName();
+            foreach ($reflectionClass->getTraits() as $traitReflectionClass) {
+                $fileNames[] = $traitReflectionClass->getFileName();
+            }
+
+            $reflectionClass = $reflectionClass->getParentClass();
+        } while ($reflectionClass instanceof ReflectionClass);
+
+        return array_filter($fileNames, is_string(...));
+    }
 }
diff --git a/tests/ChangedFilesDetector/FileHashComputer/FileHashComputerTest.php b/tests/ChangedFilesDetector/FileHashComputer/FileHashComputerTest.php
index 4dd304bf9c..7c89584b76 100644
--- a/tests/ChangedFilesDetector/FileHashComputer/FileHashComputerTest.php
+++ b/tests/ChangedFilesDetector/FileHashComputer/FileHashComputerTest.php
@@ -47,6 +47,24 @@ public function testInvalidateCacheOnConfigurationChange(): void
         $this->filesystem->remove(self::INCLUDED_CONFIG_FILE);
     }
 
+    public function testInvalidateCacheOnLocalCheckerChange(): void
+    {
+        $localSniffFile = __DIR__ . '/Source/LocalSniff.php';
+        $originalContents = $this->filesystem->readFile($localSniffFile);
+
+        $originalHash = $this->fileHashComputer->computeConfig(__DIR__ . '/Source/local_sniff_config.php');
+
+        try {
+            $this->filesystem->dumpFile($localSniffFile, $originalContents . "\n// changed\n");
+
+            $changedHash = $this->fileHashComputer->computeConfig(__DIR__ . '/Source/local_sniff_config.php');
+        } finally {
+            $this->filesystem->dumpFile($localSniffFile, $originalContents);
+        }
+
+        $this->assertNotSame($originalHash, $changedHash);
+    }
+
     public function testPhpFileHash(): void
     {
         $fileOne = __DIR__ . '/Source/SomeScannedClass.php';
diff --git a/tests/ChangedFilesDetector/FileHashComputer/Source/LocalSniff.php b/tests/ChangedFilesDetector/FileHashComputer/Source/LocalSniff.php
new file mode 100644
index 0000000000..cad44998b6
--- /dev/null
+++ b/tests/ChangedFilesDetector/FileHashComputer/Source/LocalSniff.php
@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Symplify\EasyCodingStandard\Tests\ChangedFilesDetector\FileHashComputer\Source;
+
+use PHP_CodeSniffer\Files\File;
+use PHP_CodeSniffer\Sniffs\Sniff;
+
+final class LocalSniff implements Sniff
+{
+    public function register()
+    {
+        return [T_WHILE];
+    }
+
+    public function process(File $phpcsFile, $stackPtr)
+    {
+    }
+}
diff --git a/tests/ChangedFilesDetector/FileHashComputer/Source/local_sniff_config.php b/tests/ChangedFilesDetector/FileHashComputer/Source/local_sniff_config.php
new file mode 100644
index 0000000000..2eaf68b22f
--- /dev/null
+++ b/tests/ChangedFilesDetector/FileHashComputer/Source/local_sniff_config.php
@@ -0,0 +1,9 @@
+<?php
+
+declare(strict_types=1);
+
+use Symplify\EasyCodingStandard\Config\ECSConfig;
+use Symplify\EasyCodingStandard\Tests\ChangedFilesDetector\FileHashComputer\Source\LocalSniff;
+
+return ECSConfig::configure()
+    ->withRules([LocalSniff::class]);