diff --git a/src/Immediate.Validations.Analyzers/AnalyzerReleases.Unshipped.md b/src/Immediate.Validations.Analyzers/AnalyzerReleases.Unshipped.md
index 4444261..7908ac1 100644
--- a/src/Immediate.Validations.Analyzers/AnalyzerReleases.Unshipped.md
+++ b/src/Immediate.Validations.Analyzers/AnalyzerReleases.Unshipped.md
@@ -9,3 +9,4 @@ IV0004 | ImmediateValidations | Error | ValidatorClassAnalyzer
 IV0005 | ImmediateValidations | Error | ValidatorClassAnalyzer
 IV0006 | ImmediateValidations | Error | ValidatorClassAnalyzer
 IV0007 | ImmediateValidations | Error | ValidatorClassAnalyzer
+IV0008 | ImmediateValidations | Error | ValidatorClassAnalyzer
diff --git a/src/Immediate.Validations.Analyzers/DiagnosticIds.cs b/src/Immediate.Validations.Analyzers/DiagnosticIds.cs
index 9c8a07d..764faaf 100644
--- a/src/Immediate.Validations.Analyzers/DiagnosticIds.cs
+++ b/src/Immediate.Validations.Analyzers/DiagnosticIds.cs
@@ -9,4 +9,5 @@ public static class DiagnosticIds
 	public const string IV0005ValidateMethodIsMissingParameter = "IV0005";
 	public const string IV0006ValidateMethodHasExtraParameter = "IV0006";
 	public const string IV0007ValidateMethodParameterIsIncorrectType = "IV0007";
+	public const string IV0008ValidatePropertyMustBeRequired = "IV0008";
 }
diff --git a/src/Immediate.Validations.Analyzers/ValidatorClassAnalyzer.cs b/src/Immediate.Validations.Analyzers/ValidatorClassAnalyzer.cs
index ec53c0f..4a82146 100644
--- a/src/Immediate.Validations.Analyzers/ValidatorClassAnalyzer.cs
+++ b/src/Immediate.Validations.Analyzers/ValidatorClassAnalyzer.cs
@@ -85,6 +85,17 @@ public sealed class ValidatorClassAnalyzer : DiagnosticAnalyzer
 			description: "`Validate()` parameters must exist as properties on the containing Validator class."
 		);
 
+	public static readonly DiagnosticDescriptor ValidatePropertyMustBeRequired =
+		new(
+			id: DiagnosticIds.IV0008ValidatePropertyMustBeRequired,
+			title: "Validator property must be `required`",
+			messageFormat: "Property `{0}` must have the `required` modifier",
+			category: "ImmediateValidations",
+			defaultSeverity: DiagnosticSeverity.Error,
+			isEnabledByDefault: true,
+			description: "`Validate()` parameters without a default value require values to be set on their matching properties."
+		);
+
 	public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } =
 		ImmutableArray.Create<DiagnosticDescriptor>(
 		[
@@ -95,6 +106,7 @@ public sealed class ValidatorClassAnalyzer : DiagnosticAnalyzer
 			ValidateMethodIsMissingParameter,
 			ValidateMethodHasExtraParameter,
 			ValidateMethodParameterIsIncorrectType,
+			ValidatePropertyMustBeRequired,
 		]);
 
 	public override void Initialize(AnalysisContext context)
@@ -236,6 +248,20 @@ private void AnalyzeSymbol(SymbolAnalysisContext context)
 								)
 							);
 						}
+
+						if (
+							!parameter.HasExplicitDefaultValue
+							&& !property.IsRequired
+						)
+						{
+							context.ReportDiagnostic(
+								Diagnostic.Create(
+									ValidatePropertyMustBeRequired,
+									property.Locations[0],
+									property.Name
+								)
+							);
+						}
 					}
 				}
 
diff --git a/tests/Immediate.Validations.Tests/AnalyzerTests/ValidatorClassAnalyzerTests.cs b/tests/Immediate.Validations.Tests/AnalyzerTests/ValidatorClassAnalyzerTests.cs
index d216546..96fa509 100644
--- a/tests/Immediate.Validations.Tests/AnalyzerTests/ValidatorClassAnalyzerTests.cs
+++ b/tests/Immediate.Validations.Tests/AnalyzerTests/ValidatorClassAnalyzerTests.cs
@@ -140,6 +140,33 @@ public static (bool Invalid, string? DefaultMessage) ValidateProperty(int value,
 			"""
 		).RunAsync();
 
+	[Fact]
+	public async Task ValidateMethodGeneralParameterVarianceShouldWarn() =>
+		await AnalyzerTestHelpers.CreateAnalyzerTest<ValidatorClassAnalyzer>(
+			"""
+			using Immediate.Validations.Shared;
+
+			public sealed class GreaterThanAttribute : ValidatorAttribute
+			{
+				public required int {|IV0005:Alpha|} { get; init; }
+				public required int {|IV0005:Charlie|} { get; init; }
+				public required int {|IV0005:Echo|} { get; init; }
+
+				public static (bool Invalid, string? DefaultMessage) ValidateProperty(
+					int value, 
+					int {|IV0006:bravo|},
+					int {|IV0006:delta|},
+					int {|IV0006:foxtrot|}
+				)
+				{
+					return value <= 0
+						? (true, "Property must not be `null`.")
+						: default;
+				}
+			}
+			"""
+		).RunAsync();
+
 	[Fact]
 	public async Task ValidateMethodMismatchTypesShouldWarn1() =>
 		await AnalyzerTestHelpers.CreateAnalyzerTest<ValidatorClassAnalyzer>(
@@ -179,4 +206,25 @@ public static (bool Invalid, string? DefaultMessage) ValidateProperty(string val
 			}
 			"""
 		).RunAsync();
+
+	[Fact]
+	public async Task ValidatePropertyMissingRequiredShouldWarn() =>
+		await AnalyzerTestHelpers.CreateAnalyzerTest<ValidatorClassAnalyzer>(
+			"""
+			using Immediate.Validations.Shared;
+
+			public sealed class GreaterThanAttribute : ValidatorAttribute
+			{
+				public int {|IV0008:Operand|} { get; init; }
+
+				public static (bool Invalid, string? DefaultMessage) ValidateProperty(int value, int operand)
+				{
+					return value <= operand
+						? (true, "Property must not be `null`.")
+						: default;
+				}
+			}
+			"""
+		).RunAsync();
+
 }