diff --git a/include/boost/variant2/variant.hpp b/include/boost/variant2/variant.hpp
index 3cf2dc1..5515600 100644
--- a/include/boost/variant2/variant.hpp
+++ b/include/boost/variant2/variant.hpp
@@ -1,7 +1,7 @@
 #ifndef BOOST_VARIANT2_VARIANT_HPP_INCLUDED
 #define BOOST_VARIANT2_VARIANT_HPP_INCLUDED
 
-// Copyright 2017, 2018 Peter Dimov.
+// Copyright 2017-2019 Peter Dimov.
 //
 // Distributed under the Boost Software License, Version 1.0.
 //
@@ -266,6 +266,10 @@ template<std::size_t I, class... T> struct variant_alternative<I, variant<T...>>
 
 #endif
 
+// variant_npos
+
+constexpr std::size_t variant_npos = ~static_cast<std::size_t>( 0 );
+
 // holds_alternative
 
 template<class U, class... T> constexpr bool holds_alternative( variant<T...> const& v ) noexcept
@@ -1350,6 +1354,11 @@ public:
 
     // value status
 
+    constexpr bool valueless_by_exception() const noexcept
+    {
+        return false;
+    }
+
     using variant_base::index;
 
     // swap
diff --git a/test/Jamfile b/test/Jamfile
index 7ad76a4..18642a0 100644
--- a/test/Jamfile
+++ b/test/Jamfile
@@ -1,6 +1,6 @@
 #  Boost.Variant2 Library Test Jamfile
 #
-#  Copyright 2015-2017 Peter Dimov
+#  Copyright 2015-2019 Peter Dimov
 #
 #  Distributed under the Boost Software License, Version 1.0.
 #  See accompanying file LICENSE_1_0.txt or copy at
@@ -9,7 +9,19 @@
 import testing ;
 import ../../config/checks/config : requires ;
 
-project : requirements [ requires cxx11_variadic_templates cxx11_template_aliases cxx11_decltype cxx11_constexpr ] ;
+project
+  : default-build
+
+    <warnings>all
+
+  : requirements
+
+    [ requires cxx11_variadic_templates cxx11_template_aliases cxx11_decltype cxx11_constexpr ]
+
+    <toolset>msvc:<warnings-as-errors>on
+    <toolset>gcc:<warnings-as-errors>on
+    <toolset>clang:<warnings-as-errors>on
+  ;
 
 run variant_size.cpp ;
 run variant_alternative.cpp ;
diff --git a/test/variant_convert_construct_throw.cpp b/test/variant_convert_construct_throw.cpp
index 79757fc..bb53d7c 100644
--- a/test/variant_convert_construct_throw.cpp
+++ b/test/variant_convert_construct_throw.cpp
@@ -6,6 +6,10 @@
 // See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt
 
+#if defined(_MSC_VER)
+# pragma warning( disable: 4702 ) // unreachable code
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <stdexcept>
diff --git a/test/variant_copy_assign_throw.cpp b/test/variant_copy_assign_throw.cpp
index 7f98f70..a13dccb 100644
--- a/test/variant_copy_assign_throw.cpp
+++ b/test/variant_copy_assign_throw.cpp
@@ -6,6 +6,10 @@
 // See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt
 
+#if defined(_MSC_VER)
+# pragma warning( disable: 4702 ) // unreachable code
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <stdexcept>
diff --git a/test/variant_copy_construct_throw.cpp b/test/variant_copy_construct_throw.cpp
index 88937c2..81b44d9 100644
--- a/test/variant_copy_construct_throw.cpp
+++ b/test/variant_copy_construct_throw.cpp
@@ -6,6 +6,10 @@
 // See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt
 
+#if defined(_MSC_VER)
+# pragma warning( disable: 4702 ) // unreachable code
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <stdexcept>
diff --git a/test/variant_move_assign_throw.cpp b/test/variant_move_assign_throw.cpp
index 6e65518..c1df594 100644
--- a/test/variant_move_assign_throw.cpp
+++ b/test/variant_move_assign_throw.cpp
@@ -6,6 +6,10 @@
 // See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt
 
+#if defined(_MSC_VER)
+# pragma warning( disable: 4702 ) // unreachable code
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <stdexcept>
diff --git a/test/variant_move_construct_throw.cpp b/test/variant_move_construct_throw.cpp
index 01b2b02..aabf7d2 100644
--- a/test/variant_move_construct_throw.cpp
+++ b/test/variant_move_construct_throw.cpp
@@ -6,6 +6,10 @@
 // See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt
 
+#if defined(_MSC_VER)
+# pragma warning( disable: 4702 ) // unreachable code
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <stdexcept>
diff --git a/test/variant_subset.cpp b/test/variant_subset.cpp
index 86cd505..90c9bc2 100644
--- a/test/variant_subset.cpp
+++ b/test/variant_subset.cpp
@@ -6,6 +6,10 @@
 // See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt
 
+#if defined(_MSC_VER)
+# pragma warning( disable: 4702 ) // unreachable code
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <boost/core/lightweight_test_trait.hpp>
diff --git a/test/variant_valueless.cpp b/test/variant_valueless.cpp
index 6a13086..176c674 100644
--- a/test/variant_valueless.cpp
+++ b/test/variant_valueless.cpp
@@ -6,6 +6,10 @@
 // See accompanying file LICENSE_1_0.txt or copy at
 // http://www.boost.org/LICENSE_1_0.txt
 
+#if defined(_MSC_VER)
+# pragma warning( disable: 4702 ) // unreachable code
+#endif
+
 #include <boost/variant2/variant.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <type_traits>