diff --git a/beets/mediafile.py b/beets/mediafile.py
index b25184727..7cf4ef6e3 100644
--- a/beets/mediafile.py
+++ b/beets/mediafile.py
@@ -254,7 +254,19 @@ def _image_mime_type(data):
     """Return the MIME type of the image data (a bytestring).
     """
     kind = imghdr.what(None, h=data)
-    return 'image/{0}'.format(kind)
+    if kind in ['gif', 'jpeg', 'png', 'tiff', 'bmp']:
+        return 'image/{0}'.format(kind)
+    elif kind == 'pgm':
+        return 'image/x-portable-graymap'
+    elif kind == 'pbm':
+        return 'image/x-portable-bitmap'
+    elif kind == 'ppm':
+        return 'image/x-portable-pixmap'
+    elif kind == 'xbm':
+        return 'image/x-xbitmap'
+    else:
+        return 'image/x-{0}'.format(kind)
+
 
 # StorageStyle classes describe strategies for accessing values in
 # Mutagen file objects.
diff --git a/test/test_mediafile.py b/test/test_mediafile.py
index c8e878086..e1a926530 100644
--- a/test/test_mediafile.py
+++ b/test/test_mediafile.py
@@ -186,6 +186,24 @@ class ExtendedImageStructureTestMixin(ImageStructureTestMixin):
         self.assertEqual(image.desc, desc)
         self.assertEqual(image.type, type)
 
+    def test_add_tiff_image(self):
+        mediafile = self._mediafile_fixture('image')
+        self.assertEqual(len(mediafile.images), 2)
+
+        image = Image(data=self.tiff_data, desc='the composer',
+                         type=Image.TYPES.composer)
+        mediafile.images += [image]
+        mediafile.save()
+
+        mediafile = MediaFile(mediafile.path)
+        self.assertEqual(len(mediafile.images), 3)
+
+        # WMA does not preserve the order, so we have to work around this
+        image = filter(lambda i: i.mime_type == 'image/tiff',
+                           mediafile.images)[0]
+        self.assertExtendedImageAttributes(image,
+                desc='the composer', type=Image.TYPES.composer)
+
 
 # TODO include this in ReadWriteTestBase if implemented
 class LazySaveTestMixin(object):