diff --git a/boost/program_options/variables_map.hpp b/boost/program_options/variables_map.hpp
index be0a4b6..22d59e5 100644
--- a/boost/program_options/variables_map.hpp
+++ b/boost/program_options/variables_map.hpp
@@ -62,6 +62,12 @@ namespace boost { namespace program_options {
         : v(xv), m_defaulted(xdefaulted) 
         {}
 
+        variable_value& operator=(variable_value const& other)
+            {
+                v = other.v;
+                m_defaulted = other.m_defaulted;
+                return *this;
+            }
         /** If stored value if of type T, returns that value. Otherwise,
             throws boost::bad_any_cast exception. */
        template<class T>