diff --git a/include/fc/variant_object.hpp b/include/fc/variant_object.hpp
index 55077ee..5a39c80 100644
--- a/include/fc/variant_object.hpp
+++ b/include/fc/variant_object.hpp
@@ -176,6 +176,14 @@ namespace fc
          set(std::move(key), variant( fc::forward<T>(var) ) );
          return *this;
       }
+      /**
+       * Copy a variant_object into this mutable_variant_object.
+       */
+      mutable_variant_object& operator()( const variant_object& vo );
+      /**
+       * Copy another mutable_variant_object into this mutable_variant_object.
+       */
+      mutable_variant_object& operator()( const mutable_variant_object& mvo );
       ///@}
 
 
diff --git a/src/variant_object.cpp b/src/variant_object.cpp
index f3cb488..6f3b1dc 100644
--- a/src/variant_object.cpp
+++ b/src/variant_object.cpp
@@ -350,6 +350,22 @@ namespace fc
       return *this;
    }
 
+   mutable_variant_object& mutable_variant_object::operator()( const variant_object& vo )
+   {
+      for( const variant_object::entry& e : vo )
+         set( e.key(), e.value() );
+      return *this;
+   }
+
+   mutable_variant_object& mutable_variant_object::operator()( const mutable_variant_object& mvo )
+   {
+      if( &mvo == this )     // mvo(mvo) is no-op
+         return *this;
+      for( const mutable_variant_object::entry& e : mvo )
+         set( e.key(), e.value() );
+      return *this;
+   }
+
    void to_variant( const mutable_variant_object& var,  variant& vo )
    {
       vo = variant(var);