diff --git a/src/MemoryAdapter.php b/src/MemoryAdapter.php
index 1331380..f5fe0e3 100644
--- a/src/MemoryAdapter.php
+++ b/src/MemoryAdapter.php
@@ -105,7 +105,8 @@ public function getMetadata($path)
      */
     public function getMimetype($path)
     {
-        $mimetype = Util::guessMimeType($path, $this->storage[$path]['contents']);
+        $mimetype = isset($this->storage[$path]['mimetype']) ? $this->storage[$path]['mimetype'] :
+            Util::guessMimeType($path, $this->storage[$path]['contents']);
 
         return [
             'mimetype' => $mimetype,
@@ -223,6 +224,9 @@ public function update($path, $contents, Config $config)
         $this->storage[$path]['timestamp'] = $config->get('timestamp', time());
         $this->storage[$path]['size'] = Util::contentSize($contents);
         $this->storage[$path]['visibility'] = $config->get('visibility', $this->storage[$path]['visibility']);
+        if ($config->has('mimetype')) {
+            $this->storage[$path]['mimetype'] = $config->get('mimetype');
+        }
 
         return $this->getMetadata($path);
     }
diff --git a/tests/MemoryAdapterTest.php b/tests/MemoryAdapterTest.php
index a53b206..640a9a4 100644
--- a/tests/MemoryAdapterTest.php
+++ b/tests/MemoryAdapterTest.php
@@ -82,12 +82,24 @@ public function testGetMetadata()
         $this->assertSame(8, $meta['size']);
         $this->assertSame('public', $meta['visibility']);
         $this->assertTrue(is_int($meta['timestamp']));
+
+        $this->adapter->write('dir/file.txt', '', new Config(['mimetype' => 'mime/type']));
+
+        $meta = $this->adapter->getMetadata('dir/file.txt');
+
+        $this->assertCount(6, $meta);
+        $this->assertSame('mime/type', $meta['mimetype']);
     }
 
     public function testGetMimetype()
     {
+        $this->adapter->write('dir/file.txt', 'contents', new Config(['mimetype' => 'mime/type']));
+
         $meta = $this->adapter->getMimetype('file.txt');
         $this->assertSame('text/plain', $meta['mimetype']);
+
+        $meta = $this->adapter->getMimetype('dir/file.txt');
+        $this->assertSame('mime/type', $meta['mimetype']);
     }
 
     public function testGetSize()