diff --git a/src/Caliburn.Xaml.Universal/Behaviors/TriggerAction.cs b/src/Caliburn.Xaml.Universal/Behaviors/TriggerAction.cs
index a28bd23..d82f81d 100644
--- a/src/Caliburn.Xaml.Universal/Behaviors/TriggerAction.cs
+++ b/src/Caliburn.Xaml.Universal/Behaviors/TriggerAction.cs
@@ -1,4 +1,5 @@
-using Microsoft.Xaml.Interactivity;
+using System;
+using Microsoft.Xaml.Interactivity;
 using Windows.UI.Xaml;
 
 namespace Caliburn.Light
@@ -57,6 +58,9 @@ protected virtual void OnDetaching() { }
         /// </returns>
         public object Execute(object sender, object parameter)
         {
+            if (AssociatedObject == null)
+                throw new InvalidOperationException("AssociatedObject was not set before Execute.");
+
             Invoke(parameter);
             return null;
         }