diff --git a/avatar/conf.py b/avatar/conf.py
index 1d94d6e..791a90c 100644
--- a/avatar/conf.py
+++ b/avatar/conf.py
@@ -17,7 +17,7 @@ class AvatarConf(AppConf):
     MAX_SIZE = 1024 * 1024
     THUMB_FORMAT = "PNG"
     THUMB_QUALITY = 85
-    THUMB_MODES = ["RGB", "RGBA"]
+    THUMB_MODES = ("RGB", "RGBA")
     HASH_FILENAMES = False
     HASH_USERDIRNAMES = False
     EXPOSE_USERNAMES = False
diff --git a/avatar/models.py b/avatar/models.py
index 6aa20d6..a798bae 100644
--- a/avatar/models.py
+++ b/avatar/models.py
@@ -163,7 +163,9 @@ class Avatar(models.Model):
                 else:
                     diff = int((h - w) / 2)
                     image = image.crop((0, diff, w, h - diff))
-                if image.mode not in (settings.AVATAR_THUMB_MODES):
+                if settings.AVATAR_THUMB_FORMAT == "JPEG" and image.mode == "RGBA":
+                    image = image.convert("RGB")
+                elif image.mode not in (settings.AVATAR_THUMB_MODES):
                     image = image.convert(settings.AVATAR_THUMB_MODES[0])
                 image = image.resize((size, size), settings.AVATAR_RESIZE_METHOD)
                 thumb = BytesIO()
diff --git a/docs/index.txt b/docs/index.txt
index cd652b9..b2a04ba 100644
--- a/docs/index.txt
+++ b/docs/index.txt
@@ -223,11 +223,9 @@ appear on the site. Listed below are those settings:
     "keep" (only JPEG) as provided by Pillow. Defaults to `85`.
 
 .. py:data:: AVATAR_THUMB_MODES
-    A list of acceptable modes for thumbnails as provided by Pillow. If the mode
+    A sequence of acceptable modes for thumbnails as provided by Pillow. If the mode
     of the image is not in the list, the thumbnail will be converted to the
-    first mode in the list. Note that you need to set this to modes available
-    for AVATAR_THUMB_FORMAT and JPEG does not support RGBA. Defaults to
-    `['RGB', 'RGBA']`.
+    first mode in the list. Defaults to `('RGB', 'RGBA')`.
 
 .. py:data:: AVATAR_CLEANUP_DELETED