diff --git a/notebook/files/handlers.py b/notebook/files/handlers.py
index 1da0ad71d4..02ca2f8317 100644
--- a/notebook/files/handlers.py
+++ b/notebook/files/handlers.py
@@ -57,7 +57,7 @@ def get(self, path, include_body=True):
             self.set_attachment_header(name)
         
         # get mimetype from filename
-        if name.endswith('.ipynb'):
+        if name.lower().endswith('.ipynb'):
             self.set_header('Content-Type', 'application/x-ipynb+json')
         else:
             cur_mime = mimetypes.guess_type(name)[0]