diff --git a/radicale/__init__.py b/radicale/__init__.py
index f413fa9e..fa0e0e6e 100644
--- a/radicale/__init__.py
+++ b/radicale/__init__.py
@@ -409,7 +409,10 @@ class Application:
         else:
             # Get whole collection
             answer = collection.serialize()
-            etag = collection.etag
+            if answer is None:
+                return client.NOT_FOUND, {}, None
+            else:
+                etag = collection.etag
 
         if answer:
             headers = {
diff --git a/radicale/storage.py b/radicale/storage.py
index 5e142534..37bf565e 100644
--- a/radicale/storage.py
+++ b/radicale/storage.py
@@ -543,6 +543,8 @@ class Collection(BaseCollection):
         return time.strftime("%a, %d %b %Y %H:%M:%S GMT", time.gmtime(last))
 
     def serialize(self):
+        if not os.path.exists(self._filesystem_path):
+            return None
         items = []
         for href in os.listdir(self._filesystem_path):
             path = os.path.join(self._filesystem_path, href)