diff --git a/ThScoreFileConverter.Benchmarks/Program.cs b/ThScoreFileConverter.Benchmarks/Program.cs
index 638aeb41..2c40f793 100644
--- a/ThScoreFileConverter.Benchmarks/Program.cs
+++ b/ThScoreFileConverter.Benchmarks/Program.cs
@@ -3,4 +3,4 @@
 using BenchmarkDotNet.Running;
 
 var config = DefaultConfig.Instance.AddDiagnoser(MemoryDiagnoser.Default);
-_ = BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).RunAll(config, args);
+_ = BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).RunAllJoined(config, args);
diff --git a/ThScoreFileConverter.Benchmarks/Scenarios/IsDefined.cs b/ThScoreFileConverter.Benchmarks/Scenarios/IsDefined.cs
new file mode 100644
index 00000000..1b560d40
--- /dev/null
+++ b/ThScoreFileConverter.Benchmarks/Scenarios/IsDefined.cs
@@ -0,0 +1,28 @@
+using BenchmarkDotNet.Attributes;
+using EnumHelper_ = ThScoreFileConverter.Core.Helpers.EnumHelper;
+
+namespace ThScoreFileConverter.Benchmarks.Scenarios;
+
+#pragma warning disable CA1822 // Mark members as static
+
+public class IsDefined
+{
+    [GlobalSetup]
+    public void Setup()
+    {
+        _ = Enum.IsDefined(DayOfWeek.Sunday);
+        _ = EnumHelper_.IsDefined(DayOfWeek.Sunday);
+    }
+
+    [Benchmark]
+    public bool NetCore()
+    {
+        return Enum.IsDefined(DayOfWeek.Sunday);
+    }
+
+    [Benchmark]
+    public bool EnumHelper()
+    {
+        return EnumHelper_.IsDefined(DayOfWeek.Sunday);
+    }
+}
diff --git a/ThScoreFileConverter.Core.Tests/Helpers/EnumHelperTests.cs b/ThScoreFileConverter.Core.Tests/Helpers/EnumHelperTests.cs
index 54c67c31..03694ab0 100644
--- a/ThScoreFileConverter.Core.Tests/Helpers/EnumHelperTests.cs
+++ b/ThScoreFileConverter.Core.Tests/Helpers/EnumHelperTests.cs
@@ -52,4 +52,11 @@ public void CartesianTest()
 
         CollectionAssert.That.AreEqual(expected, EnumHelper.Cartesian<Protagonist, UnnamedCharacter>());
     }
+
+    [TestMethod]
+    public void IsDefinedTest()
+    {
+        Assert.IsTrue(EnumHelper.IsDefined(DayOfWeek.Sunday));
+        Assert.IsFalse(EnumHelper.IsDefined((DayOfWeek)7));
+    }
 }
diff --git a/ThScoreFileConverter.Core/Helpers/EnumHelper.cs b/ThScoreFileConverter.Core/Helpers/EnumHelper.cs
index a2ae6da0..78f11fe1 100644
--- a/ThScoreFileConverter.Core/Helpers/EnumHelper.cs
+++ b/ThScoreFileConverter.Core/Helpers/EnumHelper.cs
@@ -47,4 +47,25 @@ public static TEnum To<TEnum>(object value)
     {
         return EnumHelper<T1>.Enumerable.Cartesian(EnumHelper<T2>.Enumerable);
     }
+
+    /// <summary>
+    /// Returns a boolean telling whether a given integral value exists in the <typeparamref name="TEnum"/> type.
+    /// </summary>
+    /// <typeparam name="TEnum">The enumeration type.</typeparam>
+    /// <param name="value">The value of a constant in <typeparamref name="TEnum"/>.</param>
+    /// <returns>
+    /// <see langword="true"/> if a given integral value exists in <typeparamref name="TEnum"/>;
+    /// <see langword="false"/> otherwise.
+    /// </returns>
+    /// <remarks>
+    /// To avoid circular references, do not call it from the following attributes
+    /// (use <see cref="Enum.IsDefined{TEnum}(TEnum)"/> instead):
+    /// <see cref="Models.PatternAttribute"/>, <see cref="Models.EnumDisplayAttribute"/>,
+    /// <see cref="Models.CharacterAttribute"/>, <see cref="Models.ShotTypeAttribute{T}"/>.
+    /// </remarks>
+    public static bool IsDefined<TEnum>(TEnum value)
+        where TEnum : struct, Enum
+    {
+        return EnumHelper<TEnum>.Members.ContainsKey(value);
+    }
 }