diff --git a/contrib/frontends/django/nntpchan/nntpchan/thumbnail.py b/contrib/frontends/django/nntpchan/nntpchan/thumbnail.py
index c379550..f376658 100644
--- a/contrib/frontends/django/nntpchan/nntpchan/thumbnail.py
+++ b/contrib/frontends/django/nntpchan/nntpchan/thumbnail.py
@@ -8,7 +8,7 @@ def generate(fname, tname, placeholder):
     """
     generate thumbnail
     """
-    ext = fname.split('.')[-1]
+    ext = fname.split('.')[-1].lower()
     cmd = None
     if ext in img_ext:
         cmd = [settings.CONVERT_PATH, '-thumbnail', '200', fname, tname]