diff --git a/src/Gtk/Perspex.Cairo/Media/FormattedTextImpl.cs b/src/Gtk/Perspex.Cairo/Media/FormattedTextImpl.cs
index 4a4ec5002a..3b08b06812 100644
--- a/src/Gtk/Perspex.Cairo/Media/FormattedTextImpl.cs
+++ b/src/Gtk/Perspex.Cairo/Media/FormattedTextImpl.cs
@@ -24,8 +24,8 @@ namespace Perspex.Cairo.Media
             TextAlignment textAlignment,
             FontWeight fontWeight)
         {
-            Contract.Requires<NullReferenceException>(context != null);
-            Contract.Requires<NullReferenceException> (text != null);
+            Contract.Requires<ArgumentNullException>(context != null);
+            Contract.Requires<ArgumentNullException> (text != null);
             Layout = new Pango.Layout(context);
             _text = text;
             Layout.SetText(text);
diff --git a/src/Perspex.Base/PerspexObject.cs b/src/Perspex.Base/PerspexObject.cs
index b742579993..7a0e211f2c 100644
--- a/src/Perspex.Base/PerspexObject.cs
+++ b/src/Perspex.Base/PerspexObject.cs
@@ -215,7 +215,7 @@ namespace Perspex
         /// <returns>A collection of <see cref="PerspexProperty"/> definitions.</returns>
         public static IEnumerable<PerspexProperty> GetRegisteredProperties(Type type)
         {
-            Contract.Requires<NullReferenceException>(type != null);
+            Contract.Requires<ArgumentNullException>(type != null);
 
             TypeInfo i = type.GetTypeInfo();
 
@@ -263,8 +263,8 @@ namespace Perspex
         /// </remarks>
         public static void Register(Type type, PerspexProperty property)
         {
-            Contract.Requires<NullReferenceException>(type != null);
-            Contract.Requires<NullReferenceException>(property != null);
+            Contract.Requires<ArgumentNullException>(type != null);
+            Contract.Requires<ArgumentNullException>(property != null);
 
             List<PerspexProperty> list;
 
@@ -300,7 +300,7 @@ namespace Perspex
         /// <param name="property">The property.</param>
         public void ClearValue(PerspexProperty property)
         {
-            Contract.Requires<NullReferenceException>(property != null);
+            Contract.Requires<ArgumentNullException>(property != null);
 
             SetValue(property, PerspexProperty.UnsetValue);
         }
@@ -312,7 +312,7 @@ namespace Perspex
         /// <returns>An observable.</returns>
         public IObservable<object> GetObservable(PerspexProperty property)
         {
-            Contract.Requires<NullReferenceException>(property != null);
+            Contract.Requires<ArgumentNullException>(property != null);
 
             return new PerspexObservable<object>(
                 observer =>
@@ -345,7 +345,7 @@ namespace Perspex
         /// <returns>An observable.</returns>
         public IObservable<T> GetObservable<T>(PerspexProperty<T> property)
         {
-            Contract.Requires<NullReferenceException>(property != null);
+            Contract.Requires<ArgumentNullException>(property != null);
 
             return GetObservable((PerspexProperty)property).Cast<T>();
         }
@@ -387,7 +387,7 @@ namespace Perspex
         /// <returns>The value.</returns>
         public object GetValue(PerspexProperty property)
         {
-            Contract.Requires<NullReferenceException>(property != null);
+            Contract.Requires<ArgumentNullException>(property != null);
 
             if (property.IsDirect)
             {
@@ -425,7 +425,7 @@ namespace Perspex
         /// <returns>The value.</returns>
         public T GetValue<T>(PerspexProperty<T> property)
         {
-            Contract.Requires<NullReferenceException>(property != null);
+            Contract.Requires<ArgumentNullException>(property != null);
 
             if (property.IsDirect)
             {
@@ -455,7 +455,7 @@ namespace Perspex
         /// <returns>True if the property is set, otherwise false.</returns>
         public bool IsSet(PerspexProperty property)
         {
-            Contract.Requires<NullReferenceException>(property != null);
+            Contract.Requires<ArgumentNullException>(property != null);
 
             return _values.ContainsKey(property);
         }
@@ -481,7 +481,7 @@ namespace Perspex
             object value,
             BindingPriority priority = BindingPriority.LocalValue)
         {
-            Contract.Requires<NullReferenceException>(property != null);
+            Contract.Requires<ArgumentNullException>(property != null);
 
             if (property.IsDirect)
             {
@@ -546,7 +546,7 @@ namespace Perspex
             T value,
             BindingPriority priority = BindingPriority.LocalValue)
         {
-            Contract.Requires<NullReferenceException>(property != null);
+            Contract.Requires<ArgumentNullException>(property != null);
 
             if (property.IsDirect)
             {
@@ -579,7 +579,7 @@ namespace Perspex
             IObservable<object> source,
             BindingPriority priority = BindingPriority.LocalValue)
         {
-            Contract.Requires<NullReferenceException>(property != null);
+            Contract.Requires<ArgumentNullException>(property != null);
 
             if (property.IsDirect)
             {
@@ -638,7 +638,7 @@ namespace Perspex
             IObservable<T> source,
             BindingPriority priority = BindingPriority.LocalValue)
         {
-            Contract.Requires<NullReferenceException>(property != null);
+            Contract.Requires<ArgumentNullException>(property != null);
 
             if (property.IsDirect)
             {
@@ -741,7 +741,7 @@ namespace Perspex
             object newValue,
             BindingPriority priority)
         {
-            Contract.Requires<NullReferenceException>(property != null);
+            Contract.Requires<ArgumentNullException>(property != null);
 
             PerspexPropertyChangedEventArgs e = new PerspexPropertyChangedEventArgs(
                 this,
diff --git a/src/Perspex.Base/PerspexProperty.cs b/src/Perspex.Base/PerspexProperty.cs
index e0f2f980b4..d612a3b285 100644
--- a/src/Perspex.Base/PerspexProperty.cs
+++ b/src/Perspex.Base/PerspexProperty.cs
@@ -74,9 +74,9 @@ namespace Perspex
             Func<PerspexObject, object, object> validate = null,
             bool isAttached = false)
         {
-            Contract.Requires<NullReferenceException>(name != null);
-            Contract.Requires<NullReferenceException>(valueType != null);
-            Contract.Requires<NullReferenceException>(ownerType != null);
+            Contract.Requires<ArgumentNullException>(name != null);
+            Contract.Requires<ArgumentNullException>(valueType != null);
+            Contract.Requires<ArgumentNullException>(ownerType != null);
 
             if (name.Contains("."))
             {
@@ -113,10 +113,10 @@ namespace Perspex
             Func<PerspexObject, object> getter,
             Action<PerspexObject, object> setter)
         {
-            Contract.Requires<NullReferenceException>(name != null);
-            Contract.Requires<NullReferenceException>(valueType != null);
-            Contract.Requires<NullReferenceException>(ownerType != null);
-            Contract.Requires<NullReferenceException>(getter != null);
+            Contract.Requires<ArgumentNullException>(name != null);
+            Contract.Requires<ArgumentNullException>(valueType != null);
+            Contract.Requires<ArgumentNullException>(ownerType != null);
+            Contract.Requires<ArgumentNullException>(getter != null);
 
             if (name.Contains("."))
             {
@@ -143,8 +143,8 @@ namespace Perspex
             Func<PerspexObject, object> getter,
             Action<PerspexObject, object> setter)
         {
-            Contract.Requires<NullReferenceException>(source != null);
-            Contract.Requires<NullReferenceException>(getter != null);
+            Contract.Requires<ArgumentNullException>(source != null);
+            Contract.Requires<ArgumentNullException>(getter != null);
 
             if (!source.IsDirect)
             {
@@ -321,7 +321,7 @@ namespace Perspex
             Func<TOwner, TValue, TValue> validate = null)
             where TOwner : PerspexObject
         {
-            Contract.Requires<NullReferenceException>(name != null);
+            Contract.Requires<ArgumentNullException>(name != null);
 
             PerspexProperty<TValue> result = new PerspexProperty<TValue>(
                 name,
@@ -352,7 +352,7 @@ namespace Perspex
             Action<TOwner, TValue> setter = null)
                 where TOwner : PerspexObject
         {
-            Contract.Requires<NullReferenceException>(name != null);
+            Contract.Requires<ArgumentNullException>(name != null);
 
             PerspexProperty<TValue> result = new PerspexProperty<TValue>(
                 name,
@@ -384,7 +384,7 @@ namespace Perspex
             BindingMode defaultBindingMode = BindingMode.OneWay,
             Func<PerspexObject, TValue, TValue> validate = null)
         {
-            Contract.Requires<NullReferenceException>(name != null);
+            Contract.Requires<ArgumentNullException>(name != null);
 
             PerspexProperty<TValue> result = new PerspexProperty<TValue>(
                 name,
@@ -420,7 +420,7 @@ namespace Perspex
             BindingMode defaultBindingMode = BindingMode.OneWay,
             Func<PerspexObject, TValue, TValue> validate = null)
         {
-            Contract.Requires<NullReferenceException>(name != null);
+            Contract.Requires<ArgumentNullException>(name != null);
 
             PerspexProperty<TValue> result = new PerspexProperty<TValue>(
                 name,
@@ -478,7 +478,7 @@ namespace Perspex
         /// <returns>The default value.</returns>
         public object GetDefaultValue(Type type)
         {
-            Contract.Requires<NullReferenceException>(type != null);
+            Contract.Requires<ArgumentNullException>(type != null);
 
             while (type != null)
             {
@@ -504,7 +504,7 @@ namespace Perspex
         /// </returns>
         public Func<PerspexObject, object, object> GetValidationFunc(Type type)
         {
-            Contract.Requires<NullReferenceException>(type != null);
+            Contract.Requires<ArgumentNullException>(type != null);
 
             while (type != null)
             {
@@ -548,7 +548,7 @@ namespace Perspex
         /// <param name="defaultValue">The default value.</param>
         public void OverrideDefaultValue(Type type, object defaultValue)
         {
-            Contract.Requires<NullReferenceException>(type != null);
+            Contract.Requires<ArgumentNullException>(type != null);
 
             if (!TypeUtilities.TryCast(PropertyType, defaultValue, out defaultValue))
             {
@@ -574,7 +574,7 @@ namespace Perspex
         /// <param name="validation">The validation function.</param>
         public void OverrideValidation(Type type, Func<PerspexObject, object, object> validation)
         {
-            Contract.Requires<NullReferenceException>(type != null);
+            Contract.Requires<ArgumentNullException>(type != null);
 
             if (_validation.ContainsKey(type))
             {
diff --git a/src/Perspex.Base/Utilities/TypeUtilities.cs b/src/Perspex.Base/Utilities/TypeUtilities.cs
index 81bd5ad250..98909d9801 100644
--- a/src/Perspex.Base/Utilities/TypeUtilities.cs
+++ b/src/Perspex.Base/Utilities/TypeUtilities.cs
@@ -35,7 +35,7 @@ namespace Perspex.Utilities
         /// <returns>True if the cast was sucessful, otherwise false.</returns>
         public static bool TryCast(Type to, object value, out object result)
         {
-            Contract.Requires<NullReferenceException>(to != null);
+            Contract.Requires<ArgumentNullException>(to != null);
 
             if (value == null)
             {
diff --git a/src/Perspex.Input/InputExtensions.cs b/src/Perspex.Input/InputExtensions.cs
index f53ecc5524..ef3f848073 100644
--- a/src/Perspex.Input/InputExtensions.cs
+++ b/src/Perspex.Input/InputExtensions.cs
@@ -11,7 +11,7 @@ namespace Perspex.Input
     {
         public static IEnumerable<IInputElement> GetInputElementsAt(this IInputElement element, Point p)
         {
-            Contract.Requires<NullReferenceException>(element != null);
+            Contract.Requires<ArgumentNullException>(element != null);
 
             if (element.Bounds.Contains(p) &&
                 element.IsVisible &&
diff --git a/src/Perspex.Interactivity/Interactive.cs b/src/Perspex.Interactivity/Interactive.cs
index 03b7c72a2d..a6bfd0d94c 100644
--- a/src/Perspex.Interactivity/Interactive.cs
+++ b/src/Perspex.Interactivity/Interactive.cs
@@ -37,8 +37,8 @@ namespace Perspex.Interactivity
             RoutingStrategies routes = RoutingStrategies.Direct | RoutingStrategies.Bubble,
             bool handledEventsToo = false)
         {
-            Contract.Requires<NullReferenceException>(routedEvent != null);
-            Contract.Requires<NullReferenceException>(handler != null);
+            Contract.Requires<ArgumentNullException>(routedEvent != null);
+            Contract.Requires<ArgumentNullException>(handler != null);
 
             List<EventSubscription> subscriptions;
 
@@ -85,8 +85,8 @@ namespace Perspex.Interactivity
         /// <param name="handler">The handler.</param>
         public void RemoveHandler(RoutedEvent routedEvent, Delegate handler)
         {
-            Contract.Requires<NullReferenceException>(routedEvent != null);
-            Contract.Requires<NullReferenceException>(handler != null);
+            Contract.Requires<ArgumentNullException>(routedEvent != null);
+            Contract.Requires<ArgumentNullException>(handler != null);
 
             List<EventSubscription> subscriptions;
 
@@ -114,7 +114,7 @@ namespace Perspex.Interactivity
         /// <param name="e">The event args.</param>
         public void RaiseEvent(RoutedEventArgs e)
         {
-            Contract.Requires<NullReferenceException>(e != null);
+            Contract.Requires<ArgumentNullException>(e != null);
 
             e.Source = e.Source ?? this;
 
@@ -141,7 +141,7 @@ namespace Perspex.Interactivity
         /// <param name="e">The event args.</param>
         private void BubbleEvent(RoutedEventArgs e)
         {
-            Contract.Requires<NullReferenceException>(e != null);
+            Contract.Requires<ArgumentNullException>(e != null);
 
             e.Route = RoutingStrategies.Bubble;
 
@@ -157,7 +157,7 @@ namespace Perspex.Interactivity
         /// <param name="e">The event args.</param>
         private void TunnelEvent(RoutedEventArgs e)
         {
-            Contract.Requires<NullReferenceException>(e != null);
+            Contract.Requires<ArgumentNullException>(e != null);
 
             e.Route = RoutingStrategies.Tunnel;
 
@@ -173,7 +173,7 @@ namespace Perspex.Interactivity
         /// <param name="e">The event args.</param>
         private void RaiseEventImpl(RoutedEventArgs e)
         {
-            Contract.Requires<NullReferenceException>(e != null);
+            Contract.Requires<ArgumentNullException>(e != null);
 
             e.RoutedEvent.InvokeClassHandlers(this, e);
 
diff --git a/src/Perspex.Interactivity/RoutedEvent.cs b/src/Perspex.Interactivity/RoutedEvent.cs
index 0b387821a4..ca865f74d0 100644
--- a/src/Perspex.Interactivity/RoutedEvent.cs
+++ b/src/Perspex.Interactivity/RoutedEvent.cs
@@ -26,9 +26,9 @@ namespace Perspex.Interactivity
             Type eventArgsType,
             Type ownerType)
         {
-            Contract.Requires<NullReferenceException>(name != null);
-            Contract.Requires<NullReferenceException>(eventArgsType != null);
-            Contract.Requires<NullReferenceException>(ownerType != null);
+            Contract.Requires<ArgumentNullException>(name != null);
+            Contract.Requires<ArgumentNullException>(eventArgsType != null);
+            Contract.Requires<ArgumentNullException>(ownerType != null);
             Contract.Requires<InvalidCastException>(typeof(RoutedEventArgs).GetTypeInfo().IsAssignableFrom(eventArgsType.GetTypeInfo()));
 
             EventArgsType = eventArgsType;
@@ -66,7 +66,7 @@ namespace Perspex.Interactivity
             RoutingStrategies routingStrategy)
                 where TEventArgs : RoutedEventArgs
         {
-            Contract.Requires<NullReferenceException>(name != null);
+            Contract.Requires<ArgumentNullException>(name != null);
 
             return new RoutedEvent<TEventArgs>(name, routingStrategy, typeof(TOwner));
         }
@@ -77,7 +77,7 @@ namespace Perspex.Interactivity
             Type ownerType)
                 where TEventArgs : RoutedEventArgs
         {
-            Contract.Requires<NullReferenceException>(name != null);
+            Contract.Requires<ArgumentNullException>(name != null);
 
             return new RoutedEvent<TEventArgs>(name, routingStrategy, ownerType);
         }
@@ -117,8 +117,8 @@ namespace Perspex.Interactivity
         public RoutedEvent(string name, RoutingStrategies routingStrategies, Type ownerType)
             : base(name, routingStrategies, typeof(TEventArgs), ownerType)
         {
-            Contract.Requires<NullReferenceException>(name != null);
-            Contract.Requires<NullReferenceException>(ownerType != null);
+            Contract.Requires<ArgumentNullException>(name != null);
+            Contract.Requires<ArgumentNullException>(ownerType != null);
         }
 
         public void AddClassHandler<TTarget>(
diff --git a/src/Perspex.SceneGraph/VisualTree/VisualExtensions.cs b/src/Perspex.SceneGraph/VisualTree/VisualExtensions.cs
index 14b24ba041..901bf678f1 100644
--- a/src/Perspex.SceneGraph/VisualTree/VisualExtensions.cs
+++ b/src/Perspex.SceneGraph/VisualTree/VisualExtensions.cs
@@ -19,7 +19,7 @@ namespace Perspex.VisualTree
         /// <returns>The visual's ancestors.</returns>
         public static IEnumerable<IVisual> GetVisualAncestors(this IVisual visual)
         {
-            Contract.Requires<NullReferenceException>(visual != null);
+            Contract.Requires<ArgumentNullException>(visual != null);
 
             visual = visual.VisualParent;
 
@@ -53,7 +53,7 @@ namespace Perspex.VisualTree
         /// <returns>The visuals at the requested point.</returns>
         public static IVisual GetVisualAt(this IVisual visual, Point p)
         {
-            Contract.Requires<NullReferenceException>(visual != null);
+            Contract.Requires<ArgumentNullException>(visual != null);
 
             return visual.GetVisualsAt(p).FirstOrDefault();
         }
@@ -66,7 +66,7 @@ namespace Perspex.VisualTree
         /// <returns>The visuals at the requested point.</returns>
         public static IEnumerable<IVisual> GetVisualsAt(this IVisual visual, Point p)
         {
-            Contract.Requires<NullReferenceException>(visual != null);
+            Contract.Requires<ArgumentNullException>(visual != null);
 
             if (visual.Bounds.Contains(p))
             {
@@ -162,7 +162,7 @@ namespace Perspex.VisualTree
         /// </returns>
         public static IVisual GetVisualRoot(this IVisual visual)
         {
-            Contract.Requires<NullReferenceException>(visual != null);
+            Contract.Requires<ArgumentNullException>(visual != null);
 
             var parent = visual.VisualParent;
 
diff --git a/src/Perspex.Styling/LogicalTree/LogicalExtensions.cs b/src/Perspex.Styling/LogicalTree/LogicalExtensions.cs
index d134330036..e36b78d42c 100644
--- a/src/Perspex.Styling/LogicalTree/LogicalExtensions.cs
+++ b/src/Perspex.Styling/LogicalTree/LogicalExtensions.cs
@@ -11,7 +11,7 @@ namespace Perspex.LogicalTree
     {
         public static IEnumerable<ILogical> GetLogicalAncestors(this ILogical logical)
         {
-            Contract.Requires<NullReferenceException>(logical != null);
+            Contract.Requires<ArgumentNullException>(logical != null);
 
             logical = logical.LogicalParent;
 
diff --git a/src/Perspex.Styling/Styling/StyleBinding.cs b/src/Perspex.Styling/Styling/StyleBinding.cs
index 61da30a842..c0235161db 100644
--- a/src/Perspex.Styling/Styling/StyleBinding.cs
+++ b/src/Perspex.Styling/Styling/StyleBinding.cs
@@ -86,7 +86,7 @@ namespace Perspex.Styling
         /// <returns>IDisposable object used to unsubscribe from the observable sequence.</returns>
         protected override IDisposable SubscribeCore(IObserver<object> observer)
         {
-            Contract.Requires<NullReferenceException>(observer != null);
+            Contract.Requires<ArgumentNullException>(observer != null);
 
             if (Source == null)
             {