diff --git a/common/protocol/address.go b/common/protocol/address.go
index a0ae63525..598352a05 100644
--- a/common/protocol/address.go
+++ b/common/protocol/address.go
@@ -61,7 +61,7 @@ func maybeIPPrefix(b byte) bool {
 
 func isValidDomain(d string) bool {
 	for _, c := range d {
-		if !((c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '-' || c == '.') {
+		if !((c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '-' || c == '.' || c == '_') {
 			return false
 		}
 	}