diff --git a/include/boost/tuple/detail/tuple_basic.hpp b/include/boost/tuple/detail/tuple_basic.hpp
index 5e3727e..1bf5966 100644
--- a/include/boost/tuple/detail/tuple_basic.hpp
+++ b/include/boost/tuple/detail/tuple_basic.hpp
@@ -581,7 +581,7 @@ namespace detail {
 struct swallow_assign {
 
   template<typename T>
-  swallow_assign& operator=(const T&) {
+  swallow_assign const& operator=(const T&) const {
     return *this;
   }
 };
diff --git a/include/boost/tuple/detail/tuple_basic_no_partial_spec.hpp b/include/boost/tuple/detail/tuple_basic_no_partial_spec.hpp
index f4cdde9..2fc5214 100644
--- a/include/boost/tuple/detail/tuple_basic_no_partial_spec.hpp
+++ b/include/boost/tuple/detail/tuple_basic_no_partial_spec.hpp
@@ -96,7 +96,7 @@ namespace tuples {
       struct swallow_assign
       {
         template<typename T>
-        swallow_assign& operator=(const T&)
+        swallow_assign const& operator=(const T&) const
         {
           return *this;
         }