diff --git a/src/net/addr/ip.cpp b/src/net/addr/ip.cpp
index 16e328f..e411054 100644
--- a/src/net/addr/ip.cpp
+++ b/src/net/addr/ip.cpp
@@ -5,4 +5,5 @@
 template In4Addr FromStr<In4Addr>::operator()(std::string_view) const;
 template char* ToStr<In4Addr>::operator()(char*, In4Addr) const noexcept;
 template In6Addr FromStr<In6Addr>::operator()(std::string_view) const;
+template char* ToStr<In6Addr>::operator()(char*, In6Addr) const noexcept;
 } // namespace stdplus