diff --git a/src/CommunityToolkit.Mvvm.SourceGenerators/ComponentModel/ObservableValidatorValidateAllPropertiesGenerator.Execute.cs b/src/CommunityToolkit.Mvvm.SourceGenerators/ComponentModel/ObservableValidatorValidateAllPropertiesGenerator.Execute.cs
index 3ff64228b..c8e097135 100644
--- a/src/CommunityToolkit.Mvvm.SourceGenerators/ComponentModel/ObservableValidatorValidateAllPropertiesGenerator.Execute.cs
+++ b/src/CommunityToolkit.Mvvm.SourceGenerators/ComponentModel/ObservableValidatorValidateAllPropertiesGenerator.Execute.cs
@@ -42,7 +42,7 @@ public static ValidationInfo GetInfo(INamedTypeSymbol typeSymbol)
         {
             using ImmutableArrayBuilder<string> propertyNames = ImmutableArrayBuilder<string>.Rent();
 
-            foreach (ISymbol memberSymbol in typeSymbol.GetMembers())
+            foreach (ISymbol memberSymbol in typeSymbol.GetAllMembers())
             {
                 if (memberSymbol is { IsStatic: true } or not (IPropertySymbol { IsIndexer: false } or IFieldSymbol))
                 {
diff --git a/src/CommunityToolkit.Mvvm.SourceGenerators/Messaging/IMessengerRegisterAllGenerator.Execute.cs b/src/CommunityToolkit.Mvvm.SourceGenerators/Messaging/IMessengerRegisterAllGenerator.Execute.cs
index 516a3bd2d..8b36b73af 100644
--- a/src/CommunityToolkit.Mvvm.SourceGenerators/Messaging/IMessengerRegisterAllGenerator.Execute.cs
+++ b/src/CommunityToolkit.Mvvm.SourceGenerators/Messaging/IMessengerRegisterAllGenerator.Execute.cs
@@ -4,7 +4,6 @@
 
 using System.Collections.Immutable;
 using System.Linq;
-using CommunityToolkit.Mvvm.SourceGenerators.ComponentModel.Models;
 using CommunityToolkit.Mvvm.SourceGenerators.Extensions;
 using CommunityToolkit.Mvvm.SourceGenerators.Helpers;
 using CommunityToolkit.Mvvm.SourceGenerators.Messaging.Models;
diff --git a/tests/CommunityToolkit.Mvvm.UnitTests/Test_ObservableValidator.cs b/tests/CommunityToolkit.Mvvm.UnitTests/Test_ObservableValidator.cs
index b686d2192..af4b9f4be 100644
--- a/tests/CommunityToolkit.Mvvm.UnitTests/Test_ObservableValidator.cs
+++ b/tests/CommunityToolkit.Mvvm.UnitTests/Test_ObservableValidator.cs
@@ -491,7 +491,7 @@ public void Test_ObservableRecipient_ValidationOnNonValidatableProperties(Type t
     {
         ObservableValidatorBase viewmodel = (ObservableValidatorBase)Activator.CreateInstance(type)!;
 
-        viewmodel.ValidateAll();
+        viewmodel.ValidateAllProperties();
     }
 
     // See: https://github.com/CommunityToolkit/WindowsCommunityToolkit/issues/4272
@@ -565,6 +565,50 @@ public void Test_ObservableValidator_WithGenericTypeParameters()
         Assert.IsFalse(model.HasErrors);
     }
 
+    // See https://github.com/CommunityToolkit/dotnet/issues/691
+    [TestMethod]
+    public void Test_ObservableValidator_ValidateAllProperties_IncludeInheritedProperties()
+    {
+        DerivedModelWithValidatableProperties model = new();
+        List<DataErrorsChangedEventArgs> events = new();
+
+        model.ErrorsChanged += (s, e) => events.Add(e);
+
+        model.ValidateAllProperties();
+
+        Assert.IsTrue(model.HasErrors);
+        Assert.IsTrue(events.Count == 2);
+
+        Assert.IsTrue(events.Any(e => e.PropertyName == nameof(DerivedModelWithValidatableProperties.Name)));
+        Assert.IsTrue(events.Any(e => e.PropertyName == nameof(DerivedModelWithValidatableProperties.Number)));
+
+        events.Clear();
+
+        model.Number = 42;
+
+        model.ValidateAllProperties();
+
+        Assert.IsTrue(model.HasErrors);
+        Assert.IsTrue(events.Count == 2);
+
+        Assert.IsTrue(events.Any(e => e.PropertyName == nameof(DerivedModelWithValidatableProperties.Name)));
+        Assert.IsTrue(events.Any(e => e.PropertyName == nameof(DerivedModelWithValidatableProperties.Number)));
+
+        Assert.AreEqual(1, model.GetErrors(nameof(DerivedModelWithValidatableProperties.Name)).Count());
+        Assert.AreEqual(0, model.GetErrors(nameof(DerivedModelWithValidatableProperties.Number)).Count());
+
+        events.Clear();
+
+        model.Name = "Bob";
+        model.Number = 80;
+
+        model.ValidateAllProperties();
+
+        Assert.IsFalse(model.HasErrors);
+        Assert.IsTrue(events.Count == 1);
+
+        Assert.IsTrue(events.Any(e => e.PropertyName == nameof(DerivedModelWithValidatableProperties.Name)));    }
+
     public class Person : ObservableValidator
     {
         private string? name;
@@ -786,9 +830,9 @@ public class ObservableValidatorBase : ObservableValidator
     {
         public int? MyDummyInt { get; set; } = 0;
 
-        public void ValidateAll()
+        public new void ValidateAllProperties()
         {
-            ValidateAllProperties();
+            base.ValidateAllProperties();
         }
     }
 
@@ -824,6 +868,17 @@ public abstract class AbstractModelWithValidatableProperty : ObservableValidator
         public string? Name { get; set; }
     }
 
+    public class DerivedModelWithValidatableProperties : AbstractModelWithValidatableProperty
+    {
+        [Range(10, 1000)]
+        public int Number { get; set; }
+
+        public new void ValidateAllProperties()
+        {
+            base.ValidateAllProperties();
+        }
+    }
+
     public class GenericPerson<T> : ObservableValidator
     {
         [Required]