diff --git a/src/CommandLine/Core/TypeConverter.cs b/src/CommandLine/Core/TypeConverter.cs
index 354c4316..8f193c46 100644
--- a/src/CommandLine/Core/TypeConverter.cs
+++ b/src/CommandLine/Core/TypeConverter.cs
@@ -129,11 +129,20 @@ private static object ToEnum(this string value, Type conversionType, bool ignore
             {
                 throw new FormatException();
             }
-            if (Enum.IsDefined(conversionType, parsedValue))
+            if (IsDefinedEx(parsedValue))
             {
                 return parsedValue;
             }
             throw new FormatException();
         }
+
+        private static bool IsDefinedEx(object enumValue)
+        {
+            char firstChar = enumValue.ToString()[0];
+            if (Char.IsDigit(firstChar) || firstChar == '-')
+                return false;
+
+            return true;
+        }
     }
 }
diff --git a/tests/CommandLine.Tests/Unit/Core/TypeConverterTests.cs b/tests/CommandLine.Tests/Unit/Core/TypeConverterTests.cs
index d9f3988c..c62a7836 100644
--- a/tests/CommandLine.Tests/Unit/Core/TypeConverterTests.cs
+++ b/tests/CommandLine.Tests/Unit/Core/TypeConverterTests.cs
@@ -16,6 +16,13 @@ enum TestEnum
             ValueB = 2
         }
 
+        [Flags]
+        enum TestFlagEnum
+        {
+            ValueA = 0x1,
+            ValueB = 0x2
+        }
+
         [Theory]
         [MemberData(nameof(ChangeType_scalars_source))]
         public void ChangeType_scalars(string testValue, Type destinationType, bool expectFail, object expectedResult)
@@ -94,6 +101,19 @@ public static IEnumerable<object[]> ChangeType_scalars_source
                     new object[] {((int) TestEnum.ValueB + 1).ToString(), typeof (TestEnum), true, null},
                     new object[] {((int) TestEnum.ValueA - 1).ToString(), typeof (TestEnum), true, null},
 
+                    new object[] {"ValueA", typeof (TestFlagEnum), false, TestFlagEnum.ValueA},
+                    new object[] {"VALUEA", typeof (TestFlagEnum), false, TestFlagEnum.ValueA},
+                    new object[] {"ValueB", typeof(TestFlagEnum), false, TestFlagEnum.ValueB},
+                    new object[] {"ValueA,ValueB", typeof (TestFlagEnum), false, TestFlagEnum.ValueA | TestFlagEnum.ValueB},
+                    new object[] {"ValueA, ValueB", typeof (TestFlagEnum), false, TestFlagEnum.ValueA | TestFlagEnum.ValueB},
+                    new object[] {"VALUEA,ValueB", typeof (TestFlagEnum), false, TestFlagEnum.ValueA | TestFlagEnum.ValueB},
+                    new object[] {((int) TestFlagEnum.ValueA).ToString(), typeof (TestFlagEnum), false, TestFlagEnum.ValueA},
+                    new object[] {((int) TestFlagEnum.ValueB).ToString(), typeof (TestFlagEnum), false, TestFlagEnum.ValueB},
+                    new object[] {((int) (TestFlagEnum.ValueA | TestFlagEnum.ValueB)).ToString(), typeof (TestFlagEnum), false, TestFlagEnum.ValueA | TestFlagEnum.ValueB},
+                    new object[] {((int) TestFlagEnum.ValueB + 2).ToString(), typeof (TestFlagEnum), true, null},
+                    new object[] {((int) TestFlagEnum.ValueA - 1).ToString(), typeof (TestFlagEnum), true, null},
+
+
                     // Failed before #339
                     new object[] {"false", typeof (int), true, 0},
                     new object[] {"true", typeof (int), true, 0}