diff --git a/annolid/gui/app.py b/annolid/gui/app.py
index ce58a32..5f51835 100644
--- a/annolid/gui/app.py
+++ b/annolid/gui/app.py
@@ -7,6 +7,7 @@
 import html
 import shutil
 import pandas as pd
+import numpy as np
 from collections import deque
 import torch
 import codecs
@@ -1218,7 +1219,7 @@ def saveLabels(self, filename):
 
         def format_shape(s):
             data = s.other_data.copy()
-            if 'zone' in s.description.lower():
+            if s.description and 'zone' in s.description.lower():
                 has_zone_shapes = True
             if len(s.points) <= 1:
                 s.shape_type = 'point'
@@ -1231,7 +1232,7 @@ def format_shape(s):
                     flags=s.flags,
                     mask=None
                     if s.mask is None
-                    else utils.img_arr_to_b64(s.mask),
+                    else utils.img_arr_to_b64(s.mask.astype(np.uint8)),
                     visible=s.visible,
                     description=s.description
                 )
diff --git a/annolid/gui/label_file.py b/annolid/gui/label_file.py
index 6e45e4f..0f75494 100644
--- a/annolid/gui/label_file.py
+++ b/annolid/gui/label_file.py
@@ -120,7 +120,7 @@ def load(self, filename):
                     description=s.get("description"),
                     group_id=s.get("group_id"),
                     mask=utils.img_b64_to_arr(
-                        s["mask"]) if s.get("mask") else None,
+                        s["mask"]).astype(bool) if s.get("mask") else None,
                     visible=s.get("visible"),
                     other_data={k: v for k,
                                 v in s.items() if k not in shape_keys},