diff --git a/forgebox/__init__.py b/forgebox/__init__.py
index 8f584e6..b4ed79e 100644
--- a/forgebox/__init__.py
+++ b/forgebox/__init__.py
@@ -1 +1 @@
-__version__ = "0.4.19"
+__version__ = "0.4.20"
diff --git a/forgebox/html.py b/forgebox/html.py
index d7f2755..80d090d 100644
--- a/forgebox/html.py
+++ b/forgebox/html.py
@@ -103,7 +103,7 @@ def deeper(x):
         return list_group_kv(x)
     if type(x) in [int, str, float, bool]:
         return x
-    if type(x) in ImageClass.__subclasses__():
+    if type(x) == ImageClass:
         return img_dom(x)
     return x
 
diff --git a/nbs/04_html.ipynb b/nbs/04_html.ipynb
index 29a9b79..9160adb 100644
--- a/nbs/04_html.ipynb
+++ b/nbs/04_html.ipynb
@@ -329,7 +329,7 @@
     "        return list_group_kv(x)\n",
     "    if type(x) in [int, str, float, bool]:\n",
     "        return x\n",
-    "    if type(x) in ImageClass.__subclasses__():\n",
+    "    if type(x) == ImageClass:\n",
     "        return img_dom(x)\n",
     "    return x\n",
     "\n",
diff --git a/settings.ini b/settings.ini
index 1b4d4fb..a58b086 100644
--- a/settings.ini
+++ b/settings.ini
@@ -7,7 +7,7 @@ author = xiaochen(ray) zhang
 author_email = b2ray2c@gmail.com
 copyright = xiaochen(ray) zhang
 branch = master
-version = 0.4.19
+version = 0.4.20
 min_python = 3.6
 audience = Developers
 language = English