diff --git a/common/protocol/address.go b/common/protocol/address.go
index 598352a0..bdd2a208 100644
--- a/common/protocol/address.go
+++ b/common/protocol/address.go
@@ -172,7 +172,7 @@ func (p *AddressParser) writeAddress(writer io.Writer, address net.Address) erro
 		}
 	case net.AddressFamilyDomain:
 		domain := address.Domain()
-		if IsDomainTooLong(domain) {
+		if isDomainTooLong(domain) {
 			return newError("Super long domain is not supported: ", domain)
 		}
 		if _, err := writer.Write([]byte{tb, byte(len(domain))}); err != nil {
diff --git a/common/protocol/headers.go b/common/protocol/headers.go
index f3c6e153..5a3a1626 100644
--- a/common/protocol/headers.go
+++ b/common/protocol/headers.go
@@ -85,6 +85,6 @@ func (sc *SecurityConfig) GetSecurityType() SecurityType {
 	return sc.Type
 }
 
-func IsDomainTooLong(domain string) bool {
+func isDomainTooLong(domain string) bool {
 	return len(domain) > 256
 }