diff --git a/src/projects/EnsureThat/Enforcers/EnumArg.cs b/src/projects/EnsureThat/Enforcers/EnumArg.cs
index 2df4f1e..8c693f3 100644
--- a/src/projects/EnsureThat/Enforcers/EnumArg.cs
+++ b/src/projects/EnsureThat/Enforcers/EnumArg.cs
@@ -1,4 +1,5 @@
 using System;
+using EnsureThat.Internals;
 using JetBrains.Annotations;
 
 namespace EnsureThat.Enforcers
@@ -7,14 +8,15 @@ public sealed class EnumArg
     {
         /// <summary>
         /// Confirms that the <paramref name="value"/> is defined in the enum <typeparamref name="T"/>.
-        /// Note that just like `Enum.IsDefined`, `Flags` based enums may be valid combination of defined values, but if the combined value
-        /// itself is not named an error will be raised. Avoid usage with `Flags` enums.
+        /// Note that just like <see cref="Enum.IsDefined(Type, object)"/>,
+        /// <see cref="FlagsAttribute"/> based enums may be valid combination of defined values, but if the combined value
+        /// itself is not named an error will be raised. Avoid usage with <see cref="FlagsAttribute"/> enums.
         /// </summary>
         /// <example>
         /// Flags example:
         /// 
         /// [Flags]
-        /// enum Abc{
+        /// enum Abc {
         ///   A = 1,
         ///   B = 2,
         ///   C = 4,
@@ -22,7 +24,7 @@ public sealed class EnumArg
         /// }
         ///
         /// Abc.A | Abc.B IsDefined=true (due to Abc.AB)
-        /// Abc.A | Abc.C IsDefined=false (A and C are both valid, the composite is valid due to `Flags` attribute, but the composite is not a named enum value
+        /// Abc.A | Abc.C IsDefined=false (A and C are both valid, the composite is valid due to <see cref="FlagsAttribute"/> attribute, but the composite is not a named enum value
         /// </example>
         public T IsDefined<T>(T value, [InvokerParameterName] string paramName = null, OptsFn optsFn = null) where T : struct, Enum
         {
@@ -37,5 +39,25 @@ public T IsDefined<T>(T value, [InvokerParameterName] string paramName = null, O
 
             return value;
         }
+
+        /// <summary>
+        /// Confirms that the <paramref name="value"/> is defined in the enum <typeparamref name="T"/>.
+        /// Supports <see cref="FlagsAttribute"/> attribute.
+        /// </summary>
+        public T IsDefinedWithFlagsSupport<T>(T value, [InvokerParameterName] string paramName = null, OptsFn optsFn = null) where T : struct, Enum
+        {
+            var isEnumDefined = EnumOf<T>.Contains(value);
+
+            if (!isEnumDefined)
+            {
+                throw Ensure.ExceptionFactory.ArgumentOutOfRangeException(
+                    string.Format(ExceptionMessages.Enum_IsValidEnum, value, EnumOf<T>.EnumType),
+                    paramName,
+                    value,
+                    optsFn);
+            }
+
+            return value;
+        }
     }
 }
\ No newline at end of file
diff --git a/src/projects/EnsureThat/Ensure.cs b/src/projects/EnsureThat/Ensure.cs
index 596c107..bc7a45a 100644
--- a/src/projects/EnsureThat/Ensure.cs
+++ b/src/projects/EnsureThat/Ensure.cs
@@ -22,7 +22,7 @@ public static class Ensure
         public static BoolArg Bool { get; } = new BoolArg();
 
         /// <summary>
-        /// Ensures for enumerables.
+        /// Ensures for enums.
         /// </summary>
         [NotNull]
         public static EnumArg Enum { get; } = new EnumArg();
diff --git a/src/projects/EnsureThat/EnsureArg.Enums.cs b/src/projects/EnsureThat/EnsureArg.Enums.cs
index 6a011f2..4337c7b 100644
--- a/src/projects/EnsureThat/EnsureArg.Enums.cs
+++ b/src/projects/EnsureThat/EnsureArg.Enums.cs
@@ -8,14 +8,15 @@ public static partial class EnsureArg
     {
         /// <summary>
         /// Confirms that the <paramref name="value"/> is defined in the enum <typeparamref name="T"/>.
-        /// Note that just like `Enum.IsDefined`, `Flags` based enums may be valid combination of defined values, but if the combined value
-        /// itself is not named an error will be raised. Avoid usage with `Flags` enums.
+        /// Note that just like <see cref="Enum.IsDefined(Type, object)"/>,
+        /// <see cref="FlagsAttribute"/> based enums may be valid combination of defined values, but if the combined value
+        /// itself is not named an error will be raised. Avoid usage with <see cref="FlagsAttribute"/> enums.
         /// </summary>
         /// <example>
         /// Flags example:
         /// 
         /// [Flags]
-        /// enum Abc{
+        /// enum Abc {
         ///   A = 1,
         ///   B = 2,
         ///   C = 4,
@@ -23,9 +24,16 @@ public static partial class EnsureArg
         /// }
         ///
         /// Abc.A | Abc.B IsDefined=true (due to Abc.AB)
-        /// Abc.A | Abc.C IsDefined=false (A and C are both valid, the composite is valid due to `Flags` attribute, but the composite is not a named enum value
+        /// Abc.A | Abc.C IsDefined=false (A and C are both valid, the composite is valid due to <see cref="FlagsAttribute"/> attribute, but the composite is not a named enum value
         /// </example>
         public static T EnumIsDefined<T>(T value, [InvokerParameterName] string paramName = null, OptsFn optsFn = null) where T : struct, Enum
             => Ensure.Enum.IsDefined(value, paramName, optsFn);
+
+        /// <summary>
+        /// Confirms that the <paramref name="value"/> is defined in the enum <typeparamref name="T"/>.
+        /// Supports <see cref="FlagsAttribute"/> attribute.
+        /// </summary>
+        public static T EnumIsDefinedWithFlagsSupport<T>(T value, [InvokerParameterName] string paramName = null, OptsFn optsFn = null) where T : struct, Enum
+            => Ensure.Enum.IsDefinedWithFlagsSupport(value, paramName, optsFn);
     }
 }
\ No newline at end of file
diff --git a/src/projects/EnsureThat/EnsureThatEnumExtensions.cs b/src/projects/EnsureThat/EnsureThatEnumExtensions.cs
index 47dd2c5..a56df1c 100644
--- a/src/projects/EnsureThat/EnsureThatEnumExtensions.cs
+++ b/src/projects/EnsureThat/EnsureThatEnumExtensions.cs
@@ -4,14 +4,15 @@ public static class EnsureThatEnumExtensions
     {
         /// <summary>
         /// Confirms that the <paramref name="param.Value"/> is defined in the enum <typeparamref name="T"/>.
-        /// Note that just like `Enum.IsDefined`, `Flags` based enums may be valid combination of defined values, but if the combined value
-        /// itself is not named an error will be raised. Avoid usage with `Flags` enums.
+        /// Note that just like <see cref="System.Enum.IsDefined(System.Type, object)"/>,
+        /// <see cref="System.FlagsAttribute"/> based enums may be valid combination of defined values, but if the combined value
+        /// itself is not named an error will be raised. Avoid usage with <see cref="System.FlagsAttribute"/> enums.
         /// </summary>
         /// <example>
         /// Flags example:
         /// 
         /// [Flags]
-        /// enum Abc{
+        /// enum Abc {
         ///   A = 1,
         ///   B = 2,
         ///   C = 4,
@@ -19,9 +20,16 @@ public static class EnsureThatEnumExtensions
         /// }
         ///
         /// Abc.A | Abc.B IsDefined=true (due to Abc.AB)
-        /// Abc.A | Abc.C IsDefined=false (A and C are both valid, the composite is valid due to `Flags` attribute, but the composite is not a named enum value
+        /// Abc.A | Abc.C IsDefined=false (A and C are both valid, the composite is valid due to `<see cref="System.FlagsAttribute"/> attribute, but the composite is not a named enum value
         /// </example>
         public static void IsDefined<T>(this in Param<T> param) where T : struct, System.Enum
             => Ensure.Enum.IsDefined(param.Value, param.Name, param.OptsFn);
+
+        /// <summary>
+        /// Confirms that the <paramref name="param.Value"/> is defined in the enum <typeparamref name="T"/>.
+        /// Supports <see cref="System.FlagsAttribute"/> attribute.
+        /// </summary>
+        public static void IsDefinedWithFlagsSupport<T>(this in Param<T> param) where T : struct, System.Enum
+            => Ensure.Enum.IsDefinedWithFlagsSupport(param.Value, param.Name, param.OptsFn);
     }
 }
\ No newline at end of file
diff --git a/src/projects/EnsureThat/Internals/EnumOf.cs b/src/projects/EnsureThat/Internals/EnumOf.cs
new file mode 100644
index 0000000..8fba3d6
--- /dev/null
+++ b/src/projects/EnsureThat/Internals/EnumOf.cs
@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+
+namespace EnsureThat.Internals
+{
+    internal static class EnumOf<T> where T : struct, Enum
+    {
+        internal static readonly Type EnumType;
+        private static readonly bool _hasFlags;
+        private static readonly List<ulong> _values;
+
+        static EnumOf()
+        {
+            EnumType = typeof(T);
+
+            _hasFlags = EnumType.GetTypeInfo().GetCustomAttributes<FlagsAttribute>(false).Any();
+
+            var enumValues = Enum.GetValues(EnumType);
+            _values = new List<ulong>(enumValues.Length);
+            foreach (var v in enumValues) 
+                _values.Add(Convert.ToUInt64(v));
+        }
+
+        internal static bool Contains(T value)
+        {
+            if (!_hasFlags)
+                return Enum.IsDefined(EnumType, value);
+
+            var raw = Convert.ToUInt64(value);
+            if (raw == 0)
+                return Enum.IsDefined(EnumType, value);
+
+            ulong sum = 0;
+
+            foreach (var val in _values)
+            {
+                if ((raw & val) == val)
+                    sum |= val;
+            }
+
+            return sum == raw;
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/tests/UnitTests/EnsureEnumParamTests.cs b/src/tests/UnitTests/EnsureEnumParamTests.cs
index 5fcc00a..909c65d 100644
--- a/src/tests/UnitTests/EnsureEnumParamTests.cs
+++ b/src/tests/UnitTests/EnsureEnumParamTests.cs
@@ -9,7 +9,53 @@ public class EnsureEnumParamTests : UnitTestBase
         [Fact]
         public void IsDefined_ShouldNotThrow()
         {
-            var item = Only1IsValid.Valid;
+            var item = Only1IsValidEnum.Valid;
+
+            ShouldNotThrow(
+                () => Ensure.Enum.IsDefined(item, ParamName),
+                () => EnsureArg.EnumIsDefined(item, ParamName),
+                () => Ensure.That(item, ParamName).IsDefined());
+        }
+
+        [Theory]
+        [InlineData((Only1IsValidEnum)2)]
+        [InlineData((Only1IsValidEnum)0)]
+        public void NotDefined_ShouldThrow(Only1IsValidEnum item)
+        {
+            ShouldThrow<ArgumentOutOfRangeException>(
+                string.Format(ExceptionMessages.Enum_IsValidEnum, item, typeof(Only1IsValidEnum)),
+                () => Ensure.Enum.IsDefined(item, ParamName),
+                () => EnsureArg.EnumIsDefined(item, ParamName),
+                () => Ensure.That(item, ParamName).IsDefined());
+        }
+
+        [Fact]
+        public void IsDefinedWithFlagsSupport_ShouldNotThrow()
+        {
+            var item = Only1IsValidEnum.Valid;
+
+            ShouldNotThrow(
+                () => Ensure.Enum.IsDefinedWithFlagsSupport(item, ParamName),
+                () => EnsureArg.EnumIsDefinedWithFlagsSupport(item, ParamName),
+                () => Ensure.That(item, ParamName).IsDefinedWithFlagsSupport());
+        }
+
+        [Theory]
+        [InlineData((Only1IsValidEnum)2)]
+        [InlineData((Only1IsValidEnum)0)]
+        public void NotDefined_Extended_ShouldThrow(Only1IsValidEnum item)
+        {
+            ShouldThrow<ArgumentOutOfRangeException>(
+                string.Format(ExceptionMessages.Enum_IsValidEnum, item, typeof(Only1IsValidEnum)),
+                () => Ensure.Enum.IsDefinedWithFlagsSupport(item, ParamName),
+                () => EnsureArg.EnumIsDefinedWithFlagsSupport(item, ParamName),
+                () => Ensure.That(item, ParamName).IsDefinedWithFlagsSupport());
+        }
+
+        [Fact]
+        public void FlagIsDefined_ShouldNotThrow_IfNotCombined()
+        {
+            var item = TestFlagsEnum.Bar;
 
             ShouldNotThrow(
                 () => Ensure.Enum.IsDefined(item, ParamName),
@@ -18,20 +64,95 @@ public void IsDefined_ShouldNotThrow()
         }
 
         [Fact]
-        public void IsNotDefined_ShouldThrow()
+        public void FlagIsDefined_ShouldThrow_IfCombined()
         {
-            var item = (Only1IsValid)2;
+            var item = TestFlagsEnum.Bar | TestFlagsEnum.Baz;
 
             ShouldThrow<ArgumentOutOfRangeException>(
-                string.Format(ExceptionMessages.Enum_IsValidEnum, item, typeof(Only1IsValid)),
+                string.Format(ExceptionMessages.Enum_IsValidEnum, item, typeof(TestFlagsEnum)),
                 () => Ensure.Enum.IsDefined(item, ParamName),
                 () => EnsureArg.EnumIsDefined(item, ParamName),
                 () => Ensure.That(item, ParamName).IsDefined());
         }
 
-        private enum Only1IsValid
+        [Fact]
+        public void FlagNotDefined_ShouldThrow()
+        {
+            var item = (TestFlagsEnum)3;
+            ShouldThrow<ArgumentOutOfRangeException>(
+                string.Format(ExceptionMessages.Enum_IsValidEnum, item, typeof(TestFlagsEnum)),
+                () => Ensure.Enum.IsDefined(item, ParamName),
+                () => EnsureArg.EnumIsDefined(item, ParamName),
+                () => Ensure.That(item, ParamName).IsDefined());
+        }
+        
+        [Theory]
+        [InlineData(TestFlagsEnum.Bar)]
+        [InlineData(TestFlagsEnum.Bar | TestFlagsEnum.Baz)]
+        public void FlagIsDefined_Extended_ShouldNotThrow(TestFlagsEnum item)
+        {
+            ShouldNotThrow(
+                () => Ensure.Enum.IsDefinedWithFlagsSupport(item, ParamName),
+                () => EnsureArg.EnumIsDefinedWithFlagsSupport(item, ParamName),
+                () => Ensure.That(item, ParamName).IsDefinedWithFlagsSupport());
+        }
+
+        [Theory]
+        [InlineData((TestFlagsEnum)4)]
+        [InlineData((TestFlagsEnum)0)]
+        public void FlagNotDefined_Extended_ShouldThrow(TestFlagsEnum item)
+        {
+            ShouldThrow<ArgumentOutOfRangeException>(
+                string.Format(ExceptionMessages.Enum_IsValidEnum, item, typeof(TestFlagsEnum)),
+                () => Ensure.Enum.IsDefinedWithFlagsSupport(item, ParamName),
+                () => EnsureArg.EnumIsDefinedWithFlagsSupport(item, ParamName),
+                () => Ensure.That(item, ParamName).IsDefinedWithFlagsSupport());
+        }
+        
+        [Theory]
+        [InlineData(TestFlagsOfWhateverPower.A)]
+        [InlineData(TestFlagsOfWhateverPower.B)]
+        [InlineData(TestFlagsOfWhateverPower.C)]
+        [InlineData(TestFlagsOfWhateverPower.A | TestFlagsOfWhateverPower.C)]
+        [InlineData(TestFlagsOfWhateverPower.B | TestFlagsOfWhateverPower.C)]
+        public void FlagOfWhateverPowerIsDefined_ShouldNotThrow(TestFlagsOfWhateverPower item)
+        {
+            ShouldNotThrow(
+                () => Ensure.Enum.IsDefinedWithFlagsSupport(item, ParamName),
+                () => EnsureArg.EnumIsDefinedWithFlagsSupport(item, ParamName),
+                () => Ensure.That(item, ParamName).IsDefinedWithFlagsSupport());
+        }
+
+        [Fact]
+        public void FlagOfWhateverPowerIsNotDefined_ShouldThrow()
+        {
+            var item = (TestFlagsOfWhateverPower)9;
+            
+            ShouldThrow<ArgumentOutOfRangeException>(
+                string.Format(ExceptionMessages.Enum_IsValidEnum, item, typeof(TestFlagsOfWhateverPower)),
+                () => Ensure.Enum.IsDefinedWithFlagsSupport(item, ParamName),
+                () => EnsureArg.EnumIsDefinedWithFlagsSupport(item, ParamName),
+                () => Ensure.That(item, ParamName).IsDefinedWithFlagsSupport());
+        }
+
+        public enum Only1IsValidEnum : byte
         {
             Valid = 1
         }
+
+        [Flags]
+        public enum TestFlagsEnum : byte
+        {
+            Bar = 1,
+            Baz = 1 << 1
+        }
+
+        [Flags]
+        public enum TestFlagsOfWhateverPower : byte
+        {
+            A = 4,
+            B = 5,
+            C = 8
+        }
     }
 }
\ No newline at end of file