diff --git a/src/FilesystemHandler.php b/src/FilesystemHandler.php
index ac9f8b5..3bae275 100644
--- a/src/FilesystemHandler.php
+++ b/src/FilesystemHandler.php
@@ -9,6 +9,41 @@ class FilesystemHandler
 {
     private $root;
 
+    /**
+     * Mapping between file extension and MIME type to send in `Content-Type` response header
+     *
+     * @var array<string,string>
+     */
+    private $mimetypes = array(
+        'atom' => 'application/atom+xml',
+        'bz2' => 'application/x-bzip2',
+        'css' => 'text/css',
+        'gif' => 'image/gif',
+        'gz' => 'application/gzip',
+        'htm' => 'text/html',
+        'html' => 'text/html',
+        'ico' => 'image/x-icon',
+        'jpeg' => 'image/jpeg',
+        'jpg' => 'image/jpeg',
+        'js' => 'text/javascript',
+        'json' => 'application/json',
+        'pdf' => 'application/pdf',
+        'png' => 'image/png',
+        'rss' => 'application/rss+xml',
+        'svg' => 'image/svg+xml',
+        'tar' => 'application/x-tar',
+        'xml' => 'application/xml',
+        'zip' => 'application/zip',
+    );
+
+    /**
+     * Assign default MIME type to send in `Content-Type` response header (same as nginx/Apache)
+     *
+     * @var string
+     * @see self::$mimetypes
+     */
+    private $defaultMimetype = 'text/plain';
+
     public function __construct(string $root)
     {
         $this->root = $root;
@@ -67,11 +102,11 @@ public function __invoke(ServerRequestInterface $request)
                 );
             }
 
-            // Assign default MIME type here (same as nginx/Apache).
-            // Should use mime database in the future with fallback to given default.
+            // Assign MIME type based on file extension (same as nginx/Apache) or fall back to given default otherwise.
             // Browers are pretty good at figuring out the correct type if no charset attribute is given.
+            $ext = \strtolower(\substr($path, \strrpos($path, '.') + 1));
             $headers = [
-                'Content-Type' => 'text/plain'
+                'Content-Type' => $this->mimetypes[$ext] ?? $this->defaultMimetype
             ];
 
             $stat = @\stat($path);
diff --git a/tests/FilesystemHandlerTest.php b/tests/FilesystemHandlerTest.php
index 25ff81a..3e8600f 100644
--- a/tests/FilesystemHandlerTest.php
+++ b/tests/FilesystemHandlerTest.php
@@ -7,7 +7,23 @@
 
 class FilesystemHandlerTest extends TestCase
 {
-    public function testInvokeWithValidPathToLicenseWillReturnResponseWithFileContents()
+    public function testInvokeWithValidPathToComposerJsonWillReturnResponseWithFileContentsAndContentType()
+    {
+        $handler = new FilesystemHandler(dirname(__DIR__));
+
+        $request = new ServerRequest('GET', '/source/composer.json');
+        $request = $request->withAttribute('path', 'composer.json');
+
+        $response = $handler($request);
+
+        /** @var ResponseInterface $response */
+        $this->assertInstanceOf(ResponseInterface::class, $response);
+        $this->assertEquals(200, $response->getStatusCode());
+        $this->assertEquals('application/json', $response->getHeaderLine('Content-Type'));
+        $this->assertEquals(file_get_contents(__DIR__ . '/../composer.json'), (string) $response->getBody());
+    }
+
+    public function testInvokeWithValidPathToLicenseWillReturnResponseWithFileContentsAndDefaultContentType()
     {
         $handler = new FilesystemHandler(dirname(__DIR__));
 
diff --git a/tests/acceptance.sh b/tests/acceptance.sh
index 533e17e..ecc1b0e 100755
--- a/tests/acceptance.sh
+++ b/tests/acceptance.sh
@@ -68,15 +68,16 @@ out=$(curl -v $base/users 2>&1);     match "HTTP/.* 404"
 out=$(curl -v $base/users/ 2>&1);    match "HTTP/.* 404"
 out=$(curl -v $base/users/a/b 2>&1); match "HTTP/.* 404"
 
-out=$(curl -v $base/LICENSE 2>&1);          match "HTTP/.* 200" && match -iP "Content-Type: text/plain[\r\n]"
-out=$(curl -v $base/source 2>&1);           match -i "Location: /source/" && match -iP "Content-Type: text/html[\r\n]"
-out=$(curl -v $base/source/ 2>&1);          match "HTTP/.* 200"
-out=$(curl -v $base/source/LICENSE 2>&1);   match "HTTP/.* 200" && match -iP "Content-Type: text/plain[\r\n]"
-out=$(curl -v $base/source/LICENSE/ 2>&1);  match -i "Location: ../LICENSE"
-out=$(curl -v $base/source/LICENSE// 2>&1); match "HTTP/.* 404"
-out=$(curl -v $base/source//LICENSE 2>&1);  match "HTTP/.* 404"
-out=$(curl -v $base/source/tests 2>&1);     match -i "Location: tests/"
-out=$(curl -v $base/source/invalid 2>&1);   match "HTTP/.* 404"
-out=$(curl -v $base/source/bin%00ary 2>&1); match "HTTP/.* 40[40]" # expects 404, but not processed with nginx (400) and Apache (404)
+out=$(curl -v $base/LICENSE 2>&1);              match "HTTP/.* 200" && match -iP "Content-Type: text/plain[\r\n]"
+out=$(curl -v $base/source 2>&1);               match -i "Location: /source/" && match -iP "Content-Type: text/html[\r\n]"
+out=$(curl -v $base/source/ 2>&1);              match "HTTP/.* 200"
+out=$(curl -v $base/source/composer.json 2>&1); match "HTTP/.* 200" && match -iP "Content-Type: application/json[\r\n]"
+out=$(curl -v $base/source/LICENSE 2>&1);       match "HTTP/.* 200" && match -iP "Content-Type: text/plain[\r\n]"
+out=$(curl -v $base/source/LICENSE/ 2>&1);      match -i "Location: ../LICENSE"
+out=$(curl -v $base/source/LICENSE// 2>&1);     match "HTTP/.* 404"
+out=$(curl -v $base/source//LICENSE 2>&1);      match "HTTP/.* 404"
+out=$(curl -v $base/source/tests 2>&1);         match -i "Location: tests/"
+out=$(curl -v $base/source/invalid 2>&1);       match "HTTP/.* 404"
+out=$(curl -v $base/source/bin%00ary 2>&1);     match "HTTP/.* 40[40]" # expects 404, but not processed with nginx (400) and Apache (404)
 
 echo "OK ($n)"