diff --git a/include/boost/charconv/detail/compute_float80.hpp b/include/boost/charconv/detail/compute_float80.hpp
index d087206..6c67ad8 100644
--- a/include/boost/charconv/detail/compute_float80.hpp
+++ b/include/boost/charconv/detail/compute_float80.hpp
@@ -170,19 +170,20 @@ inline __float128 pow2top<__float128>(std::int64_t p) noexcept
 #endif
 
 template <typename T>
-inline uint128 mask_mantissa(uint128 z) noexcept;
+inline uint128 mask_mantissa(uint256 z) noexcept;
 
 #if BOOST_CHARCONV_LDBL_BITS == 80
 
 template <typename T>
-inline uint128 mask_mantissa(uint128 z) noexcept
+inline uint128 mask_mantissa(uint256 z) noexcept
 {
-    return static_cast<uint128>(static_cast<std::uint64_t>(z));
+    static constexpr uint128 mask {0x1FFFFFFFFFFFF, UINT64_MAX};
+    return (z >> 113) & mask;
 }
 #elif BOOST_CHARCONV_LDBL_BITS == 128
 
 template <typename T>
-inline uint128 mask_mantissa(uint128 z) noexcept
+inline uint128 mask_mantissa(uint256 z) noexcept
 {
     static constexpr uint128 mask {0x1FFFFFFFFFFFF, UINT64_MAX};
     return (z >> 113) & mask;
@@ -192,7 +193,7 @@ inline uint128 mask_mantissa(uint128 z) noexcept
 
 #ifdef BOOST_CHARCONV_HAS_FLOAT128
 template <>
-inline uint128 mask_mantissa<__float128>(uint128 z) noexcept
+inline uint128 mask_mantissa<__float128>(uint256 z) noexcept
 {
     static constexpr uint128 mask {0x1FFFFFFFFFFFF, UINT64_MAX};
     return (z >> 113) & mask;
diff --git a/include/boost/charconv/detail/emulated256.hpp b/include/boost/charconv/detail/emulated256.hpp
index 625c5e6..50bfbe8 100644
--- a/include/boost/charconv/detail/emulated256.hpp
+++ b/include/boost/charconv/detail/emulated256.hpp
@@ -45,6 +45,9 @@ struct uint256
         return *this;
     }
 
+    inline friend uint256 operator&(uint256 lhs, uint256 rhs) noexcept;
+    inline friend uint256 operator&(uint256 lhs, uint128 rhs) noexcept;
+
     inline friend bool operator==(uint256 lhs, uint256 rhs) noexcept;
     inline friend bool operator==(uint256 lhs, std::uint64_t rhs) noexcept;
 
@@ -101,6 +104,16 @@ uint256 operator|(uint256 lhs, uint256 rhs) noexcept
     return {lhs.high | rhs.high, lhs.low | rhs.low};
 }
 
+uint256 operator&(uint256 lhs, uint256 rhs) noexcept
+{
+    return {lhs.high & rhs.high, lhs.low & rhs.low};
+}
+
+uint256 operator&(uint256 lhs, uint128 rhs) noexcept
+{
+    return {lhs.high, lhs.low & rhs.low};
+}
+
 bool operator==(uint256 lhs, uint256 rhs) noexcept
 {
     return lhs.high == rhs.high && lhs.low == rhs.low;