diff --git a/lib/qiniu/utils.rb b/lib/qiniu/utils.rb
index b4dc829..a4bf4ac 100755
--- a/lib/qiniu/utils.rb
+++ b/lib/qiniu/utils.rb
@@ -20,7 +20,7 @@ def urlsafe_base64_decode encoded_content
       end
 
       def encode_entry_uri(bucket, key)
-        entry_uri = bucket + ':' + key
+        entry_uri = key.nil? ? bucket : bucket + ':' + key
         urlsafe_base64_encode(entry_uri)
       end