diff --git a/src/Avalonia.Base/Data/Core/BindingExpression.cs b/src/Avalonia.Base/Data/Core/BindingExpression.cs
index d36e2d1d1b..31b8338dd6 100644
--- a/src/Avalonia.Base/Data/Core/BindingExpression.cs
+++ b/src/Avalonia.Base/Data/Core/BindingExpression.cs
@@ -221,6 +221,18 @@ internal class BindingExpression : UntypedBindingExpressionBase, IDescription, I
                 var forceUpdate = _mode == BindingMode.OneWay || _updateTargetDepth > 0;
                 ConvertAndPublishValue(value, error, forceUpdate);
             }
+            else if (IsDataValidationEnabled)
+            {
+                // In OneWayToSource mode the value must not be published to the target, but any
+                // data validation error produced when writing to the source still has to be
+                // published (or cleared) so that it can be displayed (issue #8235). Publishing
+                // UnchangedValue leaves the target's value untouched.
+                var error = dataValidationError is not null ?
+                    new BindingError(dataValidationError, BindingErrorType.DataValidationError) :
+                    null;
+
+                PublishValue(UnchangedValue, error);
+            }
         }
         else if (_mode == BindingMode.OneWayToSource && nodeIndex == _nodes.Count - 2 && value is not null)
         {
diff --git a/tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.DataValidation.cs b/tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.DataValidation.cs
index 1575bf6ad3..9889a380cc 100644
--- a/tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.DataValidation.cs
+++ b/tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.DataValidation.cs
@@ -271,6 +271,102 @@ public partial class BindingExpressionTests
         GC.KeepAlive(data);
     }
 
+    [Fact]
+    public void Indei_Validation_Updates_Data_Validation_When_Writing_To_Source_OneWayToSource()
+    {
+        // Issue #8235: validation errors should be displayed for OneWayToSource bindings.
+        var data = new IndeiViewModel();
+        var target = CreateTargetWithSource(
+            data,
+            o => o.MustBePositive,
+            enableDataValidation: true,
+            mode: BindingMode.OneWayToSource);
+
+        Assert.Equal(0, data.MustBePositive);
+        AssertNoError(target, TargetClass.IntProperty);
+
+        target.Int = 5;
+
+        Assert.Equal(5, data.MustBePositive);
+        AssertNoError(target, TargetClass.IntProperty);
+
+        target.Int = -5;
+
+        Assert.Equal(-5, data.MustBePositive);
+        AssertBindingError(target, TargetClass.IntProperty, new DataValidationException("Must be positive"), BindingErrorType.DataValidationError);
+
+        target.Int = 5;
+
+        Assert.Equal(5, data.MustBePositive);
+        AssertNoError(target, TargetClass.IntProperty);
+
+        GC.KeepAlive(data);
+    }
+
+    [Fact]
+    public void DataAnnotations_Validation_Updates_Data_Validation_When_Writing_To_Source_OneWayToSource()
+    {
+        // Issue #8235: validation attributes should be displayed for OneWayToSource bindings.
+        if (!BindingPlugins.DataValidators.Any(x => x is DataAnnotationsValidationPlugin))
+            BindingPlugins.DataValidators.Insert(0, new DataAnnotationsValidationPlugin());
+
+        var data = new DataAnnotationsViewModel();
+        var target = CreateTargetWithSource(
+            data,
+            o => o.MaxLengthString,
+            enableDataValidation: true,
+            mode: BindingMode.OneWayToSource);
+
+        target.String = "1234";
+
+        Assert.Equal("1234", data.MaxLengthString);
+        AssertNoError(target, TargetClass.StringProperty);
+
+        target.String = "123456";
+
+        Assert.Equal("123456", data.MaxLengthString);
+        AssertBindingError(
+            target,
+            TargetClass.StringProperty,
+            new DataValidationException("Too long!"),
+            BindingErrorType.DataValidationError);
+
+        GC.KeepAlive(data);
+    }
+
+    [Fact]
+    public void Conversion_Error_Is_Cleared_When_Value_Becomes_Valid_OneWayToSource()
+    {
+        // Issue #15378.
+        var data = new ViewModel();
+        var target = CreateTargetWithSource(
+            data,
+            o => o.DoubleValue,
+            targetProperty: TargetClass.ObjectProperty,
+            enableDataValidation: true,
+            mode: BindingMode.OneWayToSource);
+
+        target.Object = 5.0;
+
+        Assert.Equal(5.0, data.DoubleValue);
+        AssertNoError(target, TargetClass.ObjectProperty);
+
+        target.Object = null;
+
+        AssertBindingError(
+            target,
+            TargetClass.ObjectProperty,
+            new InvalidCastException("Could not convert '(null)' (null) to System.Double."),
+            BindingErrorType.DataValidationError);
+
+        target.Object = 5.0;
+
+        Assert.Equal(5.0, data.DoubleValue);
+        AssertNoError(target, TargetClass.ObjectProperty);
+
+        GC.KeepAlive(data);
+    }
+
     [Fact]
     public void Does_Not_Subscribe_To_Indei_Of_Intermediate_Object_In_Chain()
     {
@@ -445,6 +541,15 @@ public partial class BindingExpressionTests
             get { return _requiredString; }
             set { _requiredString = value; RaisePropertyChanged(); }
         }
+
+        private string? _maxLengthString;
+
+        [MaxLength(5, ErrorMessage = "Too long!")]
+        public string? MaxLengthString
+        {
+            get { return _maxLengthString; }
+            set { _maxLengthString = value; RaisePropertyChanged(); }
+        }
     }
 
     private class IndeiDataAnnotationsViewModel : IndeiBase