diff --git a/include/fmt/core.h b/include/fmt/core.h
index d8baed9e..db6cf669 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -390,7 +390,35 @@ template <typename T> inline auto convert_for_visit(T value) -> T {
 #endif
 #if !FMT_USE_INT128
 enum class int128_t {};
-enum class uint128_t {};
+class uint128_t {
+ private:
+  uint64_t lo_, hi_;
+  constexpr uint128_t(uint64_t hi, uint64_t lo) : lo_(lo), hi_(hi) {}
+
+ public:
+  constexpr uint128_t(uint64_t value = 0) : hi_(0), lo_(value) {}
+  explicit operator int() const { return lo_; }
+  explicit operator uint64_t() const { return lo_; }
+  friend auto operator==(const uint128_t& lhs, const uint128_t& rhs) -> bool {
+    return lhs.hi_ == rhs.hi_ && lhs.lo_ == rhs.lo_;
+  }
+  friend auto operator&(const uint128_t& lhs, const uint128_t& rhs)
+      -> uint128_t {
+    return {lhs.hi_ & rhs.hi_, lhs.lo_ & rhs.lo_};
+  }
+  friend auto operator-(const uint128_t& lhs, uint64_t rhs) -> uint128_t {
+    FMT_ASSERT(lhs.lo_ >= rhs, "");
+    return {lhs.hi_, lhs.lo_ - rhs};
+  }
+  auto operator>>(int shift) const -> uint128_t {
+    if (shift == 64) return {0, hi_};
+    return {hi_ >> shift, (hi_ << (64 - shift)) | (lo_ >> shift)};
+  }
+  auto operator<<(int shift) const -> uint128_t {
+    if (shift == 64) return {lo_, 0};
+    return {hi_ << shift | (lo_ >> (64 - shift)), (lo_ << shift)};
+  }
+};
 // Reduce template instantiations.
 template <typename T> inline auto convert_for_visit(T) -> monostate {
   return {};
@@ -1431,7 +1459,8 @@ template <typename Context> struct arg_mapper {
                       !std::is_const<remove_reference_t<T>>::value ||
                       has_fallback_formatter<U, char_type>::value> {};
 
-#if (FMT_MSC_VER != 0 && FMT_MSC_VER < 1910) || FMT_ICC_VERSION != 0 || FMT_NVCC != 0
+#if (FMT_MSC_VER != 0 && FMT_MSC_VER < 1910) || FMT_ICC_VERSION != 0 || \
+    FMT_NVCC != 0
   // Workaround a bug in MSVC and Intel (Issue 2746).
   template <typename T> FMT_CONSTEXPR FMT_INLINE auto do_map(T&& val) -> T& {
     return val;
diff --git a/include/fmt/format-inl.h b/include/fmt/format-inl.h
index b2e6a14a..87663901 100644
--- a/include/fmt/format-inl.h
+++ b/include/fmt/format-inl.h
@@ -259,7 +259,7 @@ struct fp {
     using carrier_uint = typename dragonbox::float_info<Float>::carrier_uint;
     const carrier_uint significand_mask = implicit_bit - 1;
     auto u = bit_cast<carrier_uint>(n);
-    f = u & significand_mask;
+    f = static_cast<uint64_t>(u & significand_mask);
     int biased_e =
         static_cast<int>((u & exponent_mask<Float>()) >>
                          dragonbox::float_info<Float>::significand_bits);
diff --git a/test/core-test.cc b/test/core-test.cc
index a040d241..fcc988b1 100644
--- a/test/core-test.cc
+++ b/test/core-test.cc
@@ -33,6 +33,33 @@ using testing::Return;
 #  error core-test includes format.h
 #endif
 
+TEST(uint128_test, ctor) {
+  using fmt::detail::uint128_t;
+  auto n = uint128_t();
+  EXPECT_EQ(n, 0);
+  n = uint128_t(42);
+  EXPECT_EQ(n, 42);
+  EXPECT_EQ(static_cast<uint64_t>(n), 42);
+}
+
+TEST(uint128_test, shift) {
+  auto n = fmt::detail::uint128_t(42);
+  n = n << 64;
+  EXPECT_EQ(static_cast<uint64_t>(n), 0);
+  n = n >> 64;
+  EXPECT_EQ(static_cast<uint64_t>(n), 42);
+  n = n << 62;
+  EXPECT_EQ(static_cast<uint64_t>(n >> 64), 0xa);
+  EXPECT_EQ(static_cast<uint64_t>(n), 0x8000000000000000);
+  n = n >> 62;
+  EXPECT_EQ(static_cast<uint64_t>(n), 42);
+}
+
+TEST(uint128_test, minus) {
+  auto n = fmt::detail::uint128_t(42);
+  EXPECT_EQ(n - 2, 40);
+}
+
 TEST(string_view_test, value_type) {
   static_assert(std::is_same<string_view::value_type, char>::value, "");
 }