diff --git a/src/ClassScanner/ComposerMapGenerator.php b/src/ClassScanner/ComposerMapGenerator.php
index 2e2f832..95398c5 100644
--- a/src/ClassScanner/ComposerMapGenerator.php
+++ b/src/ClassScanner/ComposerMapGenerator.php
@@ -64,11 +64,21 @@ private function convertToClassMap(ClassMap $classMap, array $composerMap): Clas
 
     public function update(ClassMap $classMap, array $updatedFiles): ClassMap
     {
+        $deleted = [];
+        $skip = [];
+
         $shouldFullGenerate = false;
         foreach ($updatedFiles as $index => $updatedFile) {
             if ($this->basePath !== '' && \str_starts_with($updatedFile, $this->basePath)) {
-                $updatedFiles[$index] = \substr($updatedFile, \strlen($this->basePath));
-                $shouldFullGenerate = $shouldFullGenerate || $classMap->isAttributeClassFile($updatedFiles[$index]);
+                $checkFile = \substr($updatedFile, \strlen($this->basePath));
+
+                if (!\is_file($updatedFile)) {
+                    $deleted[] = $checkFile;
+                } else {
+                    $shouldFullGenerate = $shouldFullGenerate || $classMap->isAttributeClassFile($checkFile);
+                }
+
+                $updatedFiles[$index] = $checkFile;
             }
         }
 
@@ -76,18 +86,9 @@ public function update(ClassMap $classMap, array $updatedFiles): ClassMap
             return $this->generate();
         }
 
-        $deleted = [];
-        $skip = [];
-
         foreach ($classMap->getFiles() as $file) {
             if (!\in_array($file, $updatedFiles, true)) {
-                $skip[$file] = true;
-            }
-        }
-
-        foreach ($updatedFiles as $file) {
-            if (!\is_file($file)) {
-                $deleted[] = $file;
+                $skip[$this->basePath . $file] = true;
             }
         }
 
@@ -101,9 +102,14 @@ public function update(ClassMap $classMap, array $updatedFiles): ClassMap
             $generator->scanPaths($path, $this->excluded);
         }
 
-        $classMap = $this->convertToClassMap(
-            new ClassMap($this->paths, $this->basePath),
-            $generator->getClassMap()->getMap()
+        $classMap = $classMap->merge(
+            $this->convertToClassMap(
+                new ClassMap(
+                    $this->paths,
+                    $this->basePath
+                ),
+                $generator->getClassMap()->getMap()
+            )
         );
 
         foreach ($deleted as $filename) {
@@ -112,4 +118,4 @@ public function update(ClassMap $classMap, array $updatedFiles): ClassMap
 
         return $classMap;
     }
-}
\ No newline at end of file
+}
diff --git a/tests/ClassScanner/ComposerMapGeneratorTest.php b/tests/ClassScanner/ComposerMapGeneratorTest.php
index a26d1b1..c23f11f 100644
--- a/tests/ClassScanner/ComposerMapGeneratorTest.php
+++ b/tests/ClassScanner/ComposerMapGeneratorTest.php
@@ -31,7 +31,7 @@ protected function tearDown(): void
 
     public function testAddingClass()
     {
-        $generator = new ComposerMapGenerator([__DIR__ . '/../Fake', $this->dir]);
+        $generator = new ComposerMapGenerator([__DIR__ . '/../Fake', $this->dir], $this->dir);
 
         $classSuffix = \bin2hex(\random_bytes(4));
         $newClassName = 'CacheTest\\NewFile' . $classSuffix;
@@ -48,10 +48,7 @@ public function testAddingClass()
 
     public function testRemovingClass()
     {
-        $generator = new ComposerMapGenerator([
-            __DIR__ . '/../Fake',
-            $this->dir
-        ]);
+        $generator = new ComposerMapGenerator([__DIR__ . '/../Fake', $this->dir], $this->dir);
 
         $classSuffix = \bin2hex(\random_bytes(4));
         $newClassName = 'CacheTest\\NewFile' . $classSuffix;
@@ -66,6 +63,21 @@ public function testRemovingClass()
         $this->assertNotContains($newClassName, $classMap2->getClasses());
     }
 
+    public function testUpdateClass()
+    {
+        $generator = new ComposerMapGenerator([__DIR__ . '/../Fake', $this->dir], $this->dir);
+
+        $classSuffix = \bin2hex(\random_bytes(4));
+        $newClassName = 'CacheTest\\NewFile' . $classSuffix;
+        $this->createRandomClassFile($newClassName);
+
+        $classMap = $generator->generate();
+        $this->assertContains($newClassName, $classMap->getClasses());
+
+        $classMap2 = $generator->update($classMap, [$this->dir . '/NewFile' . $classSuffix . '.php']);
+        $this->assertContains($newClassName, $classMap2->getClasses());
+    }
+
     private function createRandomClassFile(string $className, int $value = 0): string
     {
         $bareName = \array_reverse(\explode('\\', $className))[0];