diff --git a/src/net/addr/ip.cpp b/src/net/addr/ip.cpp
index 466c509..81d2a4a 100644
--- a/src/net/addr/ip.cpp
+++ b/src/net/addr/ip.cpp
@@ -1 +1,6 @@
 #include <stdplus/net/addr/ip.hpp>
+
+namespace stdplus
+{
+template In4Addr FromStr<In4Addr>::operator()(std::string_view) const;
+}