diff --git a/ryu/ofproto/ofproto_v1_2_parser.py b/ryu/ofproto/ofproto_v1_2_parser.py
index 359e93ca..7e446176 100644
--- a/ryu/ofproto/ofproto_v1_2_parser.py
+++ b/ryu/ofproto/ofproto_v1_2_parser.py
@@ -993,7 +993,7 @@ class OFPInstructionWriteMetadata(OFPInstruction):
     metadata_mask    Metadata write bitmask
     ================ ======================================================
     """
-    def __init__(self, metadata, metadata_mask, len_=None):
+    def __init__(self, metadata, metadata_mask, type_=None, len_=None):
         super(OFPInstructionWriteMetadata, self).__init__()
         self.type = ofproto.OFPIT_WRITE_METADATA
         self.len = ofproto.OFP_INSTRUCTION_WRITE_METADATA_SIZE