diff --git a/CodeJam.Main.Tests/EnumHelperTests.cs b/CodeJam.Main.Tests/EnumHelperTests.cs
index 58f0d4959..8ca5ad064 100644
--- a/CodeJam.Main.Tests/EnumHelperTests.cs
+++ b/CodeJam.Main.Tests/EnumHelperTests.cs
@@ -40,7 +40,7 @@ private enum Flags : byte
 			D = 0x8,
 			// ReSharper disable once InconsistentNaming
 			CD = C | D,
-			Dx = D | 0x20
+			Dx = D | 0x20,
 		}
 
 		private const Flags Ab = Flags.A | Flags.B;
@@ -77,15 +77,15 @@ private enum NoFlags : byte
 		private const NoFlags EfU = NoFlags.E | NoFlags.F | NoFlagsUndef;
 		// ReSharper restore BitwiseOperatorOnEnumWithoutFlags
 
-		public enum NameDescEnum
+		public enum NameDescEnum : long
 		{
 			[Display(Name = "Field 1", Description = "Field 1 Desc")]
-			Field1,
+			Field1 = long.MinValue,
 
 			[Display]
-			Field2,
+			Field2 = 0,
 
-			Field3
+			Field3 = long.MaxValue
 		}
 		#endregion
 
@@ -425,5 +425,21 @@ public static void TestSetOrClearFlag()
 		[TestCase(NameDescEnum.Field2, ExpectedResult = "Field2")]
 		[TestCase(NameDescEnum.Field3, ExpectedResult = "Field3")]
 		public string TestGetDisplay(NameDescEnum value) => EnumHelper.GetEnumValue(value).ToString();
+
+		[Test]
+		public void TestNegativeValues()
+		{
+			IsTrue(EnumHelper.IsDefined(NameDescEnum.Field1));
+			IsFalse(EnumHelper.IsFlagsEnum<NameDescEnum>());
+			AreEqual(
+				NameDescEnum.Field1,
+				EnumHelper.TryParse<NameDescEnum>(nameof(NameDescEnum.Field1)));
+			AreEqual(
+				NameDescEnum.Field1,
+				EnumHelper.TryParse<NameDescEnum>(long.MinValue.ToString()));
+			AreEqual(
+				"Field2, Field3, Field1",
+				EnumHelper.GetNameValues<NameDescEnum>().Select(kvp => kvp.Key).Join(", "));
+		}
 	}
 }
\ No newline at end of file
diff --git a/CodeJam.Main/EnumHelper.Holder.cs b/CodeJam.Main/EnumHelper.Holder.cs
index 6ba59d509..248ddb7b9 100644
--- a/CodeJam.Main/EnumHelper.Holder.cs
+++ b/CodeJam.Main/EnumHelper.Holder.cs
@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
@@ -93,6 +94,27 @@ private static TEnum[] GetNonDefaultFlagsCore() =>
 					.Distinct()
 					.ToArray();
 
+			private static ulong ToUInt64(object value)
+			{
+				switch (Convert.GetTypeCode(value))
+				{
+					case TypeCode.Boolean:
+					case TypeCode.Char:
+					case TypeCode.Byte:
+					case TypeCode.UInt16:
+					case TypeCode.UInt32:
+					case TypeCode.UInt64:
+						return Convert.ToUInt64(value, CultureInfo.InvariantCulture);
+					case TypeCode.SByte:
+					case TypeCode.Int16:
+					case TypeCode.Int32:
+					case TypeCode.Int64:
+						return unchecked((ulong)Convert.ToInt64(value, CultureInfo.InvariantCulture));
+					default:
+						throw CodeExceptions.UnexpectedArgumentValue(nameof(value), value);
+				}
+			}
+
 			// NB: simple implementation here
 			// as result of method call is cached.
 			private static TEnum[] GetNonDefaultUniqueFlagsCore()
@@ -100,7 +122,7 @@ private static TEnum[] GetNonDefaultUniqueFlagsCore()
 				// THANKSTO: Maciej Hehl, https://stackoverflow.com/a/2709523
 				static int GetNumberOfSetBits(TEnum value)
 				{
-					var i = Convert.ToUInt64(value);
+					var i = ToUInt64(value);
 					i -= (i >> 1) & 0x5555555555555555UL;
 					i = (i & 0x3333333333333333UL) + ((i >> 2) & 0x3333333333333333UL);
 					return (int)(unchecked(((i + (i >> 4)) & 0xF0F0F0F0F0F0F0FUL) * 0x101010101010101UL) >> 56);