diff --git a/include/CppCore.Test/Math/BigInt.h b/include/CppCore.Test/Math/BigInt.h
index 9a020f5e..89c03367 100644
--- a/include/CppCore.Test/Math/BigInt.h
+++ b/include/CppCore.Test/Math/BigInt.h
@@ -205,6 +205,7 @@ namespace CppCore { namespace Test { namespace Math
       }
       INLINE static bool todouble128()
       {
+         /*
          // test low 64-bit ones that can be tested with double chast
          for (uint64_t i = 0; i <= 0x000000000000FFFFULL; i++)
          {
@@ -244,7 +245,7 @@ namespace CppCore { namespace Test { namespace Math
 
          if (!specials128)
             return false;
-
+         */
          return true;
       }
 
diff --git a/include/CppCore.Test/Math/Util.h b/include/CppCore.Test/Math/Util.h
index 65b61bec..5c117e63 100644
--- a/include/CppCore.Test/Math/Util.h
+++ b/include/CppCore.Test/Math/Util.h
@@ -1415,6 +1415,18 @@ namespace CppCore { namespace Test { namespace Math
          if (!specials)
             return false;
 
+         // test some other special cases
+         uint64_t x = 0U;
+         for (size_t i = 0; i < 64U; i++)
+         {
+            x <<= 1;
+            x |= 1;
+            double d1 = CppCore::todouble(x);
+            double d2 = (double)x;
+            if (d1 != d2)
+               return false;
+         }
+
          // test some random ones
          CppCore::Random::Default64 rnd;
          for (size_t i = 0; i < 100000; i++)
diff --git a/include/CppCore/Math/BigInt.h b/include/CppCore/Math/BigInt.h
index 5fbe4268..0d9816fb 100644
--- a/include/CppCore/Math/BigInt.h
+++ b/include/CppCore/Math/BigInt.h
@@ -2575,8 +2575,9 @@ namespace CppCore
 
       /// <summary>
       /// Convert to IEEE-754 Double Precision
+      /// TODO: This has bugs and should not be used
       /// </summary>
-      constexpr INLINE explicit operator double () const
+      /*constexpr INLINE explicit operator double() const
       {
          constexpr uint32_t BITS = N8 * 8U;
          constexpr uint32_t LOSS = BITS - 52U;
@@ -2602,10 +2603,10 @@ namespace CppCore
          los = man & LMSK;
          man >>= LOSS;
          man += ((los > LCMP) || ((los == LCMP) && ((uint32_t)man & 1U)));
-         exp |= (uint64_t)man;
+         exp |= (uint64_t)man; // this needs refactoring, see CppCore::todouble()
 
          return reinterpret_cast<double&>(exp);
-      }
+      }*/
 
       /// <summary>
       /// Convert to Decimal String
diff --git a/include/CppCore/Math/Util.h b/include/CppCore/Math/Util.h
index b145774c..5aab1c2b 100644
--- a/include/CppCore/Math/Util.h
+++ b/include/CppCore/Math/Util.h
@@ -1536,7 +1536,7 @@ namespace CppCore
       // build the zero (positive) sign bit and the exponent bits
       // exp is neg for 0-1022, zero for 1023 and pos above.
       // shift the exponent in place (52 bits mantissa)
-      const uint64_t exp = (uint64_t)(IH + 1023U) << 52;
+      uint64_t exp = (uint64_t)(IH + 1023U) << 52;
       
       // start mantissa building by left-shifting the high bit out of x.
       // this removes it and creates a fixed offset to the hidden highbit position in IEEE-754.
@@ -1572,18 +1572,17 @@ namespace CppCore
       case FE_TONEAREST:
          // round up for upper range (break tie by only rounding odd up)
          man += ((lost > 2048U) | ((lost == 2048U) & man & 1U));
-
-         //if (_bittest((long*)&lost, 11))
-         //   man += ((lost & 2047) | (man & 1)) != 0;
-
-         // if rounding overflowed into exp bits, increment exponent and remove overflow bit.
-         // disabled because just ORing the overflow into exp below gives same result here.
-         //if (man & MASKEXP) { exp++; man &= MASKMAN; }
          break;
       }
 
+      // if rounding overflowed into exp bits,
+      // increment exponent and remove overflow bit from mantissa
+      if (man & MASKEXP) {
+         exp += MASKHHI;
+         man &= MASKMAN;
+      }
+
       // combine the exponent bits with the mantissa bits
-      // OR a possible overflow bit of mantissa into exponent
       const uint64_t ri = exp | man;
       return reinterpret_cast<const double&>(ri);
    }