diff --git a/src/config/NServiceBus.Config/Configure.cs b/src/config/NServiceBus.Config/Configure.cs
index 09572c356db..6973da694b6 100644
--- a/src/config/NServiceBus.Config/Configure.cs
+++ b/src/config/NServiceBus.Config/Configure.cs
@@ -178,9 +178,6 @@ public static Configure With(IEnumerable<Type> typesToScan)
 
             TypesToScan = typesToScan;
 
-            ExtensionMethods.IsMessageTypeAction =
-                    t => typeof(IMessage).IsAssignableFrom(t) && typeof(IMessage) != t;
-
             return instance;
         }
 
diff --git a/src/core/NServiceBus/ExtensionMethods.cs b/src/core/NServiceBus/ExtensionMethods.cs
index cba478c5e95..73252da4372 100644
--- a/src/core/NServiceBus/ExtensionMethods.cs
+++ b/src/core/NServiceBus/ExtensionMethods.cs
@@ -238,7 +238,7 @@ public static void CopyHeaderFromRequest(this object msg, string key)
         /// <summary>
         /// The function used to determine whether a type is a message type.
         /// </summary>
-        public static Func<Type, bool> IsMessageTypeAction { get; set; }
+        public static Func<Type, bool> IsMessageTypeAction = t => typeof(IMessage).IsAssignableFrom(t) && typeof(IMessage) != t;
 
 
         /// <summary>
diff --git a/src/impl/Serializers/NServiceBus.Serializers.XML.Test/SerializerTests.cs b/src/impl/Serializers/NServiceBus.Serializers.XML.Test/SerializerTests.cs
index a6b9cf82052..6a65f195540 100644
--- a/src/impl/Serializers/NServiceBus.Serializers.XML.Test/SerializerTests.cs
+++ b/src/impl/Serializers/NServiceBus.Serializers.XML.Test/SerializerTests.cs
@@ -20,12 +20,6 @@ public class SerializerTests
         private int number = 1;
         private int numberOfIterations = 100;
 
-        [SetUp]
-        public void Setup()
-        {
-            NServiceBus.ExtensionMethods.IsMessageTypeAction = t => typeof(IMessage).IsAssignableFrom(t) && t != typeof(IMessage);
-        }
-
         [Test]
         public void Generic_properties_should_be_supported()
         {
diff --git a/src/impl/Serializers/NServiceBus.Serializers.XML.Test/SerializingArrayTests.cs b/src/impl/Serializers/NServiceBus.Serializers.XML.Test/SerializingArrayTests.cs
index f9794a87efd..32007b5ba95 100644
--- a/src/impl/Serializers/NServiceBus.Serializers.XML.Test/SerializingArrayTests.cs
+++ b/src/impl/Serializers/NServiceBus.Serializers.XML.Test/SerializingArrayTests.cs
@@ -24,11 +24,6 @@ public MessageWithArray(Guid sagaId, int[] someInts)
     [TestFixture]
     public class SerializingArrayTests
     {
-        [SetUp]
-        public void Setup()
-        {
-            NServiceBus.ExtensionMethods.IsMessageTypeAction = t => typeof (IMessage).IsAssignableFrom(t) && t != typeof(IMessage);
-        }
 
         [Test]
         public void CanDeserializeXmlWithWhitespace()
diff --git a/src/testing/NServiceBus.Testing.Tests/TestHandlerFixture.cs b/src/testing/NServiceBus.Testing.Tests/TestHandlerFixture.cs
index d552eb0c33e..bd96a71e9dd 100644
--- a/src/testing/NServiceBus.Testing.Tests/TestHandlerFixture.cs
+++ b/src/testing/NServiceBus.Testing.Tests/TestHandlerFixture.cs
@@ -10,7 +10,6 @@ public class TestHandlerFixture
         public void TestFixtureSetUp()
         {
             Test.Initialize(typeof(IMessage).Assembly, typeof(TestHandlerFixture).Assembly);
-            ExtensionMethods.IsMessageTypeAction = t => typeof (IMessage).IsAssignableFrom(t) && t != typeof (IMessage);
         }
 
         [Test]
diff --git a/src/unicast/NServiceBus.Unicast.Tests/Contexts/using_the_unicastbus.cs b/src/unicast/NServiceBus.Unicast.Tests/Contexts/using_the_unicastbus.cs
index 8e19152033b..098b62771b9 100644
--- a/src/unicast/NServiceBus.Unicast.Tests/Contexts/using_the_unicastbus.cs
+++ b/src/unicast/NServiceBus.Unicast.Tests/Contexts/using_the_unicastbus.cs
@@ -37,7 +37,6 @@ public void SetUp()
             {
             }
 
-            ExtensionMethods.IsMessageTypeAction = t => typeof(IMessage).IsAssignableFrom(t) && t != typeof(IMessage);
             ExtensionMethods.GetStaticOutgoingHeadersAction = () => MessageHeaderManager.staticHeaders;
             gatewayAddress = masterNodeAddress.SubScope("gateway");