diff --git a/src/StrongOf.FluentValidation/StrongStringValidators.cs b/src/StrongOf.FluentValidation/StrongStringValidators.cs
index d9d93aa..8b648df 100644
--- a/src/StrongOf.FluentValidation/StrongStringValidators.cs
+++ b/src/StrongOf.FluentValidation/StrongStringValidators.cs
@@ -46,7 +46,7 @@ public static class StrongStringValidators
     /// <returns>The rule builder options.</returns>
     public static IRuleBuilderOptions<T, TStrong?> HasMaximumLength<T, TStrong>(this IRuleBuilder<T, TStrong?> rule, int maxLength)
         where TStrong : StrongString<TStrong>
-        => rule.Must(content => content?.Value is not null && content.Value.Length <= maxLength);
+        => rule.Must(content => content?.Value is null ? true : content.Value.Length <= maxLength);
 
     /// <summary>
     /// Validates that the strong string matches a regular expression.
diff --git a/tests/StrongOf.FluentValidation.UnitTests/StrongStringValidatorsTests.cs b/tests/StrongOf.FluentValidation.UnitTests/StrongStringValidatorsTests.cs
index a5a940c..dea4393 100644
--- a/tests/StrongOf.FluentValidation.UnitTests/StrongStringValidatorsTests.cs
+++ b/tests/StrongOf.FluentValidation.UnitTests/StrongStringValidatorsTests.cs
@@ -49,6 +49,16 @@ public void HasMaximumLength_ShouldFail_WhenLengthIsGreaterThanMaxLength()
         result.ShouldHaveValidationErrorFor(x => x.Strong);
     }
 
+    [Fact]
+    public void HasMaximumLength_ShouldNotFail_WhenValueIsNull()
+    {
+        _validator.RuleFor(x => x.Strong).HasMaximumLength(5);
+
+        TestModel model = new() { Strong = null };
+        TestValidationResult<TestModel> result = _validator.TestValidate(model);
+        result.ShouldNotHaveValidationErrorFor(x => x.Strong);
+    }
+
     [Fact]
     public void IsRegexMatch_ShouldFail_WhenValueDoesNotMatchRegex()
     {