diff --git a/src/Avalonia.Animation/Animators/Animator`1.cs b/src/Avalonia.Animation/Animators/Animator`1.cs
index d784227620..23afa76bf6 100644
--- a/src/Avalonia.Animation/Animators/Animator`1.cs
+++ b/src/Avalonia.Animation/Animators/Animator`1.cs
@@ -79,15 +79,15 @@ namespace Avalonia.Animation.Animators
 
             T oldValue, newValue;
 
-            if (firstKeyframe.isNeutral)
-                oldValue = neutralValue;
+            if (!firstKeyframe.isNeutral && firstKeyframe.Value is T firstKeyframeValue)
+                oldValue = firstKeyframeValue;
             else
-                oldValue = (T)firstKeyframe.Value;
+                oldValue = neutralValue;
 
-            if (lastKeyframe.isNeutral)
-                newValue = neutralValue;
+            if (!lastKeyframe.isNeutral && lastKeyframe.Value is T lastKeyframeValue)
+                newValue = lastKeyframeValue;
             else
-                newValue = (T)lastKeyframe.Value;
+                newValue = neutralValue;
 
             if (lastKeyframe.KeySpline != null)
                 progress = lastKeyframe.KeySpline.GetSplineProgress(progress);
diff --git a/src/Avalonia.Themes.Default/Expander.xaml b/src/Avalonia.Themes.Default/Expander.xaml
index 7df65677b6..e72ddea163 100644
--- a/src/Avalonia.Themes.Default/Expander.xaml
+++ b/src/Avalonia.Themes.Default/Expander.xaml
@@ -15,7 +15,7 @@
                 BorderThickness="{TemplateBinding BorderThickness}"
                 CornerRadius="{TemplateBinding CornerRadius}">
           <Grid RowDefinitions="Auto,*">
-            <ToggleButton Name="PART_toggle" Grid.Row="0"  Content="{TemplateBinding Header}" IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
+            <ToggleButton Name="PART_toggle" Grid.Row="0" Content="{TemplateBinding Header}" IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
             <ContentPresenter Name="PART_ContentPresenter"
                               Grid.Row="1"
                               IsVisible="{TemplateBinding IsExpanded}"
@@ -32,9 +32,12 @@
   <Style Selector="Expander[ExpandDirection=Up]">
     <Setter Property="Template">
       <ControlTemplate>
-        <Border Background="{TemplateBinding Background}">
+        <Border Background="{TemplateBinding Background}"
+                BorderBrush="{TemplateBinding BorderBrush}"
+                BorderThickness="{TemplateBinding BorderThickness}"
+                CornerRadius="{TemplateBinding CornerRadius}">
           <Grid RowDefinitions="*,Auto">
-            <ToggleButton Name="PART_toggle" Grid.Row="1"  Content="{TemplateBinding Header}" IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
+            <ToggleButton Name="PART_toggle" Grid.Row="1" Content="{TemplateBinding Header}" IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
             <ContentPresenter Name="PART_ContentPresenter"
                               Grid.Row="0"
                               IsVisible="{TemplateBinding IsExpanded}"
@@ -51,9 +54,12 @@
   <Style Selector="Expander[ExpandDirection=Right]">
     <Setter Property="Template">
       <ControlTemplate>
-        <Border Background="{TemplateBinding Background}">
+        <Border Background="{TemplateBinding Background}"
+                BorderBrush="{TemplateBinding BorderBrush}"
+                BorderThickness="{TemplateBinding BorderThickness}"
+                CornerRadius="{TemplateBinding CornerRadius}">
           <Grid ColumnDefinitions="Auto,*">
-            <ToggleButton Name="PART_toggle" Grid.Column="0"  Content="{TemplateBinding Header}" IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
+            <ToggleButton Name="PART_toggle" Grid.Column="0" Content="{TemplateBinding Header}" IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
             <ContentPresenter Name="PART_ContentPresenter"
                               Grid.Column="1"
                               IsVisible="{TemplateBinding IsExpanded}"
@@ -70,9 +76,12 @@
   <Style Selector="Expander[ExpandDirection=Left]">
     <Setter Property="Template">
       <ControlTemplate>
-        <Border Background="{TemplateBinding Background}">
+        <Border Background="{TemplateBinding Background}"
+                BorderBrush="{TemplateBinding BorderBrush}"
+                BorderThickness="{TemplateBinding BorderThickness}"
+                CornerRadius="{TemplateBinding CornerRadius}">
           <Grid ColumnDefinitions="*,Auto">
-            <ToggleButton Name="PART_toggle" Grid.Column="1"  Content="{TemplateBinding Header}" IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
+            <ToggleButton Name="PART_toggle" Grid.Column="1" Content="{TemplateBinding Header}" IsChecked="{TemplateBinding IsExpanded, Mode=TwoWay}" />
             <ContentPresenter Name="PART_ContentPresenter"
                               Grid.Column="0"
                               IsVisible="{TemplateBinding IsExpanded}"
diff --git a/tests/Avalonia.Animation.UnitTests/AnimatableTests.cs b/tests/Avalonia.Animation.UnitTests/AnimatableTests.cs
index b01fb70f58..26d8059eec 100644
--- a/tests/Avalonia.Animation.UnitTests/AnimatableTests.cs
+++ b/tests/Avalonia.Animation.UnitTests/AnimatableTests.cs
@@ -1,5 +1,7 @@
 using System;
+using Avalonia.Animation.Animators;
 using Avalonia.Controls;
+using Avalonia.Controls.Shapes;
 using Avalonia.Data;
 using Avalonia.Layout;
 using Avalonia.Media;
@@ -100,6 +102,71 @@ namespace Avalonia.Animation.UnitTests
                 Times.Never);
         }
 
+
+        [Theory]
+        [InlineData(null)] //null value
+        [InlineData("stringValue")] //string value
+        public void Invalid_Values_In_Animation_Should_Not_Crash_Animations(object invalidValue)
+        {
+            var keyframe1 = new KeyFrame()
+            {
+                Setters =
+                {
+                    new Setter(Layoutable.WidthProperty, 1d),
+                },
+                KeyTime = TimeSpan.FromSeconds(0)
+            };
+
+            var keyframe2 = new KeyFrame()
+            {
+                Setters =
+                {
+                    new Setter(Layoutable.WidthProperty, 2d),
+                },
+                KeyTime = TimeSpan.FromSeconds(2),
+            };
+
+            var keyframe3 = new KeyFrame()
+            {
+                Setters =
+                {
+                    new Setter(Layoutable.WidthProperty, invalidValue),
+                },
+                KeyTime = TimeSpan.FromSeconds(3),
+            };
+
+            var animation = new Animation()
+            {
+                Duration = TimeSpan.FromSeconds(3),
+                Children =
+                {
+                    keyframe1,
+                    keyframe2,
+                    keyframe3
+                },
+                IterationCount = new IterationCount(5),
+                PlaybackDirection = PlaybackDirection.Alternate,
+            };
+
+            var rect = new Rectangle()
+            {
+                Width = 11,
+            };
+
+            var originalValue = rect.Width;
+
+            var clock = new TestClock();
+            var animationRun = animation.RunAsync(rect, clock);
+
+            clock.Step(TimeSpan.Zero);
+            Assert.Equal(rect.Width, 1);
+            clock.Step(TimeSpan.FromSeconds(2));
+            Assert.Equal(rect.Width, 2);
+            clock.Step(TimeSpan.FromSeconds(3));
+            //here we have invalid value so value should be expected and set to initial original value
+            Assert.Equal(rect.Width, originalValue);
+        }
+
         [Fact]
         public void Transition_Is_Not_Applied_When_StyleTrigger_Changes_With_LocalValue_Present()
         {