diff --git a/externals/mcl/CMakeLists.txt b/externals/mcl/CMakeLists.txt
index 49327646..5b0cfa29 100644
--- a/externals/mcl/CMakeLists.txt
+++ b/externals/mcl/CMakeLists.txt
@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.12 FATAL_ERROR)
 include(GNUInstallDirs)
 
-project(mcl LANGUAGES CXX VERSION 0.1.4)
+project(mcl LANGUAGES CXX VERSION 0.1.5)
 
 # Project options
 option(MCL_WARNINGS_AS_ERRORS "Warnings as errors" ON)
diff --git a/externals/mcl/include/mcl/bit/bit_field.hpp b/externals/mcl/include/mcl/bit/bit_field.hpp
index 71d8b4a8..c09eda0a 100644
--- a/externals/mcl/include/mcl/bit/bit_field.hpp
+++ b/externals/mcl/include/mcl/bit/bit_field.hpp
@@ -31,7 +31,7 @@ constexpr T ones(size_t count) {
     if (count == 0) {
         return 0;
     }
-    return ~static_cast<T>(0) >> (bitsizeof<T> - count);
+    return static_cast<T>(~static_cast<T>(0)) >> (bitsizeof<T> - count);
 }
 
 /// Create a mask of type T for bits [begin_bit, end_bit] inclusive.
diff --git a/externals/mcl/tests/CMakeLists.txt b/externals/mcl/tests/CMakeLists.txt
index 1b60518d..1619f34c 100644
--- a/externals/mcl/tests/CMakeLists.txt
+++ b/externals/mcl/tests/CMakeLists.txt
@@ -1,4 +1,5 @@
 add_executable(mcl-tests
+    bit/bit_field_tests.cpp
     main.cpp
     mp/metavalue_tests.cpp
     mp/typelist_tests.cpp
diff --git a/externals/mcl/tests/bit/bit_field_tests.cpp b/externals/mcl/tests/bit/bit_field_tests.cpp
new file mode 100644
index 00000000..fba31eb5
--- /dev/null
+++ b/externals/mcl/tests/bit/bit_field_tests.cpp
@@ -0,0 +1,41 @@
+// This file is part of the mcl project.
+// Copyright (c) 2022 merryhime
+// SPDX-License-Identifier: MIT
+
+#include <array>
+#include <tuple>
+
+#include <catch2/catch.hpp>
+#include <mcl/bit/bit_field.hpp>
+#include <mcl/stdint.hpp>
+
+TEST_CASE("mcl::bit::ones", "[bit]") {
+    const std::array cases{
+        std::make_tuple<size_t, u8>(0, 0x00),
+        std::make_tuple<size_t, u8>(1, 0x01),
+        std::make_tuple<size_t, u8>(2, 0x03),
+        std::make_tuple<size_t, u8>(3, 0x07),
+        std::make_tuple<size_t, u8>(4, 0x0f),
+        std::make_tuple<size_t, u8>(5, 0x1f),
+        std::make_tuple<size_t, u8>(6, 0x3f),
+        std::make_tuple<size_t, u8>(7, 0x7f),
+        std::make_tuple<size_t, u8>(8, 0xff),
+    };
+
+    for (const auto [count, expected] : cases) {
+        REQUIRE(mcl::bit::ones<u8>(count) == expected);
+        REQUIRE(mcl::bit::ones<u16>(count) == expected);
+        REQUIRE(mcl::bit::ones<u32>(count) == expected);
+        REQUIRE(mcl::bit::ones<u64>(count) == expected);
+        REQUIRE(mcl::bit::ones<uptr>(count) == expected);
+        REQUIRE(mcl::bit::ones<size_t>(count) == expected);
+    }
+}
+
+static_assert(mcl::bit::ones<3, u8>() == 0x7);
+static_assert(mcl::bit::ones<15, u16>() == 0x7fff);
+static_assert(mcl::bit::ones<16, u16>() == 0xffff);
+static_assert(mcl::bit::ones<31, u32>() == 0x7fff'ffff);
+static_assert(mcl::bit::ones<32, u32>() == 0xffff'ffff);
+static_assert(mcl::bit::ones<63, u64>() == 0x7fff'ffff'ffff'ffff);
+static_assert(mcl::bit::ones<64, u64>() == 0xffff'ffff'ffff'ffff);