diff --git a/Perspex.UnitTests/Perspex.UnitTests.csproj b/Perspex.UnitTests/Perspex.UnitTests.csproj
index c462e9c134..1e9eec4ba5 100644
--- a/Perspex.UnitTests/Perspex.UnitTests.csproj
+++ b/Perspex.UnitTests/Perspex.UnitTests.csproj
@@ -76,7 +76,7 @@
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="PerspexObjectTests.cs" />
     <Compile Include="StyleTests.cs" />
-    <Compile Include="Styling\ActivatorTests.cs" />
+    <Compile Include="Styling\StyleActivatorTests.cs" />
     <Compile Include="Styling\SelectorTests_Multiple.cs" />
     <Compile Include="Styling\SelectorTests_Class.cs" />
     <Compile Include="Styling\SelectorTests_Id.cs" />
diff --git a/Perspex.UnitTests/Styling/ActivatorTests.cs b/Perspex.UnitTests/Styling/StyleActivatorTests.cs
similarity index 85%
rename from Perspex.UnitTests/Styling/ActivatorTests.cs
rename to Perspex.UnitTests/Styling/StyleActivatorTests.cs
index 14e9ab0c94..79e8eb8c73 100644
--- a/Perspex.UnitTests/Styling/ActivatorTests.cs
+++ b/Perspex.UnitTests/Styling/StyleActivatorTests.cs
@@ -1,4 +1,5 @@
-namespace Perspex.UnitTests.Styling
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+namespace Perspex.UnitTests.Styling
 {
     using System;
     using System.Collections.Generic;
@@ -9,16 +10,15 @@
     using System.Threading.Tasks;
     using Microsoft.VisualStudio.TestTools.UnitTesting;
     using Perspex.Styling;
-    using Activator = Perspex.Styling.StyleActivator;
 
     [TestClass]
-    public class ActivatorTests
+    public class StyleActivatorTests
     {
         [TestMethod]
         public void Activator_And_Should_Follow_Single_Input()
         {
             var inputs = new[] { new TestSubject<bool>(false) };
-            var target = new Activator(inputs, ActivatorMode.And);
+            var target = new StyleActivator(inputs, ActivatorMode.And);
             var result = new TestObserver<bool>();
 
             target.Subscribe(result);
@@ -42,7 +42,7 @@
                 new TestSubject<bool>(false),
                 new TestSubject<bool>(true),
             };
-            var target = new Activator(inputs, ActivatorMode.And);
+            var target = new StyleActivator(inputs, ActivatorMode.And);
             var result = new TestObserver<bool>();
 
             target.Subscribe(result);
@@ -67,7 +67,7 @@
                 new TestSubject<bool>(false),
                 new TestSubject<bool>(true),
             };
-            var target = new Activator(inputs, ActivatorMode.And);
+            var target = new StyleActivator(inputs, ActivatorMode.And);
             var result = new TestObserver<bool>();
 
             target.Subscribe(result);
@@ -93,7 +93,7 @@
                 new TestSubject<bool>(false),
                 new TestSubject<bool>(true),
             };
-            var target = new Activator(inputs, ActivatorMode.And);
+            var target = new StyleActivator(inputs, ActivatorMode.And);
             var result = new TestObserver<bool>();
 
             target.Subscribe(result);
@@ -110,7 +110,7 @@
         public void Activator_Or_Should_Follow_Single_Input()
         {
             var inputs = new[] { new TestSubject<bool>(false) };
-            var target = new Activator(inputs, ActivatorMode.Or);
+            var target = new StyleActivator(inputs, ActivatorMode.Or);
             var result = new TestObserver<bool>();
 
             target.Subscribe(result);
@@ -134,7 +134,7 @@
                 new TestSubject<bool>(false),
                 new TestSubject<bool>(true),
             };
-            var target = new Activator(inputs, ActivatorMode.Or);
+            var target = new StyleActivator(inputs, ActivatorMode.Or);
             var result = new TestObserver<bool>();
 
             target.Subscribe(result);
@@ -158,7 +158,7 @@
                 new TestSubject<bool>(false),
                 new TestSubject<bool>(true),
             };
-            var target = new Activator(inputs, ActivatorMode.Or);
+            var target = new StyleActivator(inputs, ActivatorMode.Or);
             var result = new TestObserver<bool>();
 
             target.Subscribe(result);
@@ -183,7 +183,7 @@
                 new TestSubject<bool>(false),
                 new TestSubject<bool>(true),
             };
-            var target = new Activator(inputs, ActivatorMode.Or);
+            var target = new StyleActivator(inputs, ActivatorMode.Or);
             var result = new TestObserver<bool>();
 
             target.Subscribe(result);
@@ -196,5 +196,21 @@
             Assert.AreEqual(1, inputs[1].SubscriberCount);
             Assert.AreEqual(1, inputs[2].SubscriberCount);
         }
+
+        [TestMethod]
+        public void Completed_Activator_Should_Signal_OnCompleted()
+        {
+            var inputs = new[]
+            {
+                Observable.Return(false),
+            };
+
+            var target = new StyleActivator(inputs, ActivatorMode.Or);
+            var completed = false;
+
+            target.Subscribe(_ => { }, () => completed = true);
+
+            Assert.IsTrue(completed);
+        }
     }
 }
diff --git a/Perspex/Styling/Style.cs b/Perspex/Styling/Style.cs
index f8b9fc1546..6c8999f646 100644
--- a/Perspex/Styling/Style.cs
+++ b/Perspex/Styling/Style.cs
@@ -43,11 +43,21 @@ namespace Perspex.Styling
             string description = "Style " + this.Selector.ToString();
             StyleActivator activator = this.Selector.GetActivator(control);
 
-            if (!(activator.CurrentValue == false && activator.HasCompleted))
+            if (activator.CurrentValue || !activator.HasCompleted)
             {
+                IObservable<bool> observable = activator;
+
+                // If the activator has completed, then we want its value to be true forever.
+                // Because of this we can't pass the activator directly as it will complete 
+                // immediately and remove the binding.
+                if (activator.HasCompleted)
+                {
+                    observable = Observable.Never<bool>().StartWith(true);
+                }
+
                 foreach (Setter setter in this.Setters)
                 {
-                    StyleBinding binding = new StyleBinding(activator, setter.Value, description);
+                    StyleBinding binding = new StyleBinding(observable, setter.Value, description);
                     control.Bind(setter.Property, binding, this.Selector.Priority);
                 }
             }
diff --git a/Perspex/Styling/StyleActivator.cs b/Perspex/Styling/StyleActivator.cs
index faa55d87d8..9bb406392a 100644
--- a/Perspex/Styling/StyleActivator.cs
+++ b/Perspex/Styling/StyleActivator.cs
@@ -21,26 +21,25 @@ namespace Perspex.Styling
     {
         private ActivatorMode mode;
 
-        private List<bool> values = new List<bool>();
+        private bool[] values;
 
         private List<IDisposable> subscriptions = new List<IDisposable>();
 
         private List<IObserver<bool>> observers = new List<IObserver<bool>>();
 
         public StyleActivator(
-            IEnumerable<IObservable<bool>> inputs, 
+            IList<IObservable<bool>> inputs, 
             ActivatorMode mode = ActivatorMode.And)
         {
             int i = 0;
 
             this.mode = mode;
+            this.values = new bool[inputs.Count];
 
             foreach (IObservable<bool> input in inputs)
             {
                 int capturedIndex = i;
 
-                this.values.Add(false);
-
                 IDisposable subscription = input.Subscribe(
                     x => this.Update(capturedIndex, x),
                     x => this.Finish(capturedIndex),
@@ -79,9 +78,18 @@ namespace Perspex.Styling
         {
             Contract.Requires<ArgumentNullException>(observer != null);
 
-            this.observers.Add(observer);
             observer.OnNext(this.CurrentValue);
-            return Disposable.Create(() => this.observers.Remove(observer));
+
+            if (this.HasCompleted)
+            {
+                observer.OnCompleted();
+                return Disposable.Empty;
+            }
+            else
+            {
+                this.observers.Add(observer);
+                return Disposable.Create(() => this.observers.Remove(observer));
+            }
         }
 
         private void Update(int index, bool value)
@@ -111,10 +119,14 @@ namespace Perspex.Styling
 
         private void Finish(int i)
         {
-            // If the observable has finished on 'false' and we're in And mode then it will never 
-            // go back to true so we can unsubscribe from all the other subscriptions now. 
-            // Similarly in Or mode; if the completed value is true then we're done.
-            bool unsubscribe = this.mode == ActivatorMode.And ? !this.values[i] : this.values[i];
+            // We can unsubscribe from everything if the completed observable:
+            // - Is the only subscription.
+            // - Has finished on 'false' and we're in And mode 
+            // - Has finished on 'true' and we're in Or mode
+            var value = this.values[i];
+            var unsubscribe = 
+                (this.values.Length == 1) ||
+                (this.mode == ActivatorMode.And ? !value : value);
 
             if (unsubscribe)
             {
diff --git a/Perspex/Styling/StyleBinding.cs b/Perspex/Styling/StyleBinding.cs
index 365588b8de..622f667017 100644
--- a/Perspex/Styling/StyleBinding.cs
+++ b/Perspex/Styling/StyleBinding.cs
@@ -15,15 +15,14 @@ namespace Perspex.Styling
     /// <remarks>
     /// This class takes an activator and a value. The activator is an observable which produces
     /// a bool. When the activator produces true, this observable will produce <see cref="Value"/>.
-    /// When the activator produces false (and before the activator returns a value) it will 
-    /// produce <see cref="PerspexProperty.UnsetValue"/>.
+    /// When the activator produces false it will produce <see cref="PerspexProperty.UnsetValue"/>.
     /// </remarks>
     internal class StyleBinding : IObservable<object>, IObservableDescription
     {
         /// <summary>
-        /// The subject that provides the observable implementation.
+        /// The activator.
         /// </summary>
-        private BehaviorSubject<object> subject = new BehaviorSubject<object>(PerspexProperty.UnsetValue);
+        private IObservable<bool> activator;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="StyleBinding"/> class.
@@ -36,13 +35,9 @@ namespace Perspex.Styling
             object activatedValue,
             string description)
         {
+            this.activator = activator;
             this.ActivatedValue = activatedValue;
             this.Description = description;
-
-            activator.Subscribe(
-                active => this.subject.OnNext(active ? this.ActivatedValue : PerspexProperty.UnsetValue),
-                error => this.subject.OnError(error),
-                () => this.subject.OnCompleted());
         }
 
         /// <summary>
@@ -71,7 +66,10 @@ namespace Perspex.Styling
         public IDisposable Subscribe(IObserver<object> observer)
         {
             Contract.Requires<NullReferenceException>(observer != null);
-            return this.subject.Subscribe(observer);
+            return this.activator.Subscribe(
+                active => observer.OnNext(active ? this.ActivatedValue : PerspexProperty.UnsetValue),
+                observer.OnError,
+                observer.OnCompleted);
         }
     }
 }
diff --git a/Perspex/Styling/Styler.cs b/Perspex/Styling/Styler.cs
index e56bc9e66c..1d1932f486 100644
--- a/Perspex/Styling/Styler.cs
+++ b/Perspex/Styling/Styler.cs
@@ -18,7 +18,12 @@ namespace Perspex.Styling
         {
             IVisual visual = control as IVisual;
             IStyled styleContainer = visual.GetVisualAncestorOrSelf<IStyled>();
-            Application.Current.Styles.Attach(control);
+
+            if (Application.Current != null)
+            {
+                Application.Current.Styles.Attach(control);
+            }
+
             this.ApplyStyles(control, styleContainer);
         }