diff --git a/protob/types.proto b/protob/types.proto
index 2fb82bf2e6..339e66b988 100644
--- a/protob/types.proto
+++ b/protob/types.proto
@@ -133,7 +133,7 @@ message CoinType {
 	optional uint32 address_type_p2sh = 5 [default=5];
 	optional uint32 address_type_p2wpkh = 6 [default=6];
 	optional uint32 address_type_p2wsh = 7 [default=10];
-	optional bytes signed_message_header = 8;
+	optional string signed_message_header = 8;
 }
 
 /**