diff --git a/src/net/IPv6Address.hxx b/src/net/IPv6Address.hxx
index 2b5cfdccf..d8b9f7478 100644
--- a/src/net/IPv6Address.hxx
+++ b/src/net/IPv6Address.hxx
@@ -124,7 +124,7 @@ public:
 	 * Return a downcasted reference to the address.  This call is
 	 * only legal after verifying SocketAddress::GetFamily().
 	 */
-	static constexpr const IPv6Address &Cast(const SocketAddress src) noexcept {
+	static constexpr const IPv6Address &Cast(const SocketAddress &src) noexcept {
 		/* this reinterpret_cast works because this class is
 		   just a wrapper for struct sockaddr_in6 */
 		return *(const IPv6Address *)(const void *)src.GetAddress();