diff --git a/boost/serialization/strong_typedef.hpp b/boost/serialization/strong_typedef.hpp
--- a/boost/serialization/strong_typedef.hpp
+++ b/boost/serialization/strong_typedef.hpp
@@ -44,6 +44,7 @@
operator const T&() const {return t;} \
operator T&() {return t;} \
bool operator==(const D& rhs) const {return t == rhs.t;} \
+ bool operator==(const T& lhs) const {return t == lhs;} \
bool operator<(const D& rhs) const {return t < rhs.t;} \
};