diff --git a/openolt.proto b/openolt.proto
index 5207bb6..0e39040 100644
--- a/openolt.proto
+++ b/openolt.proto
@@ -121,10 +121,10 @@
     fixed32 src_ip = 12;
     fixed32 src_port = 13;
     fixed32 dst_port = 14;
-    string pkt_tag_type = 15;	// untagged, single, double
+    string pkt_tag_type = 15;	// untagged, single-tag, double-tag
 }
 
-message ActionCmd { 
+message ActionCmd {
     bool add_outer_tag = 1;
     bool remove_outer_tag = 2;
     bool trap_to_host = 3;