diff --git a/samples/XamlTestApplicationPcl/TestScrollable.cs b/samples/XamlTestApplicationPcl/TestScrollable.cs
index 9a0bc8de73..cc5552375b 100644
--- a/samples/XamlTestApplicationPcl/TestScrollable.cs
+++ b/samples/XamlTestApplicationPcl/TestScrollable.cs
@@ -9,17 +9,12 @@ namespace XamlTestApplication
     public class TestScrollable : Control, IScrollable
     {
         private int itemCount = 100;
-        private Action _invalidateScroll;
         private Size _extent;
         private Vector _offset;
         private Size _viewport;
         private Size _lineSize;
 
-        public Action InvalidateScroll
-        {
-            get { return _invalidateScroll; }
-            set { _invalidateScroll = value; }
-        }
+        public Action InvalidateScroll { get; set; }
 
         Size IScrollable.Extent
         {
@@ -28,10 +23,7 @@ namespace XamlTestApplication
 
         Vector IScrollable.Offset
         {
-            get
-            {
-                return _offset;
-            }
+            get { return _offset; }
 
             set
             {
@@ -64,8 +56,8 @@ namespace XamlTestApplication
         protected override Size ArrangeOverride(Size finalSize)
         {
             _viewport = new Size(finalSize.Width, finalSize.Height / _lineSize.Height);
-            _extent = new Size(_lineSize.Width, itemCount);
-            InvalidateScroll();
+            _extent = new Size(_lineSize.Width, itemCount + 1);
+            InvalidateScroll?.Invoke();
             return finalSize;
         }
 
diff --git a/src/Perspex.Controls/Primitives/IScrollable.cs b/src/Perspex.Controls/Primitives/IScrollable.cs
index 65adadb15e..752c02685d 100644
--- a/src/Perspex.Controls/Primitives/IScrollable.cs
+++ b/src/Perspex.Controls/Primitives/IScrollable.cs
@@ -12,12 +12,17 @@ namespace Perspex.Controls.Primitives
     public interface IScrollable
     {
         /// <summary>
-        /// Gets or sets the invalidation method which notifies the attached 
-        /// <see cref="ScrollViewer"/> of a change in <see cref="Extent"/> or <see cref="Offset"/>.
+        /// Gets or sets the scroll invalidation method.
         /// </summary>
         /// <remarks>
+        /// <para>
+        /// This method notifies the attached <see cref="ScrollViewer"/> of a change in 
+        /// the <see cref="Extent"/>, <see cref="Offset"/> or <see cref="Viewport"/> properties.
+        /// </para>
+        /// <para>
         /// This property is set by the parent <see cref="ScrollViewer"/> when the 
         /// <see cref="IScrollable"/> is placed inside it.
+        /// </para>
         /// </remarks>
         Action InvalidateScroll { get; set; }