diff --git a/openolt.proto b/openolt.proto
index 0e39040..2d26d66 100644
--- a/openolt.proto
+++ b/openolt.proto
@@ -121,7 +121,7 @@
     fixed32 src_ip = 12;
     fixed32 src_port = 13;
     fixed32 dst_port = 14;
-    string pkt_tag_type = 15;	// untagged, single-tag, double-tag
+    string pkt_tag_type = 15;	// untagged, single_tag, double_tag
 }
 
 message ActionCmd {