diff --git a/lib/fluent/plugin/buffer/file_single_chunk.rb b/lib/fluent/plugin/buffer/file_single_chunk.rb
index 4cc9d6c625..1ac62291f9 100644
--- a/lib/fluent/plugin/buffer/file_single_chunk.rb
+++ b/lib/fluent/plugin/buffer/file_single_chunk.rb
@@ -243,11 +243,11 @@ def file_rename(file, old_path, new_path, callback = nil)
         def encode_key(metadata)
           k = @key ? metadata.variables[@key] : metadata.tag
           k ||= ''
-          URI::DEFAULT_PARSER.escape(k, ESCAPE_REGEXP)
+          URI::RFC2396_PARSER.escape(k, ESCAPE_REGEXP)
         end
 
         def decode_key(key)
-          URI::DEFAULT_PARSER.unescape(key)
+          URI::RFC2396_PARSER.unescape(key)
         end
 
         def create_new_chunk(path, metadata, perm)