diff --git a/src/Paramore.Brighter.MessagingGateway.AWSSQS/SqsSubscription.cs b/src/Paramore.Brighter.MessagingGateway.AWSSQS/SqsSubscription.cs
index af0a30daf6..e179c30da7 100644
--- a/src/Paramore.Brighter.MessagingGateway.AWSSQS/SqsSubscription.cs
+++ b/src/Paramore.Brighter.MessagingGateway.AWSSQS/SqsSubscription.cs
@@ -125,7 +125,7 @@ public SqsSubscription(
             int requeueCount = -1,
             TimeSpan? requeueDelay = null,
             int unacceptableMessageLimit = 0,
-            MessagePumpType messagePumpType = MessagePumpType.Proactor,
+            MessagePumpType messagePumpType = MessagePumpType.Unknown,
             IAmAChannelFactory? channelFactory = null,
             int lockTimeout = 10,
             int delaySeconds = 0,
diff --git a/src/Paramore.Brighter.MessagingGateway.AzureServiceBus/AzureServiceBusSubscription.cs b/src/Paramore.Brighter.MessagingGateway.AzureServiceBus/AzureServiceBusSubscription.cs
index d3522b3ae0..4503df7a2c 100644
--- a/src/Paramore.Brighter.MessagingGateway.AzureServiceBus/AzureServiceBusSubscription.cs
+++ b/src/Paramore.Brighter.MessagingGateway.AzureServiceBus/AzureServiceBusSubscription.cs
@@ -65,7 +65,7 @@ public AzureServiceBusSubscription(
         int requeueCount = -1,
         TimeSpan? requeueDelay = null,
         int unacceptableMessageLimit = 0,
-        MessagePumpType messagePumpType = MessagePumpType.Proactor,
+        MessagePumpType messagePumpType = MessagePumpType.Unknown,
         IAmAChannelFactory? channelFactory = null,
         OnMissingChannel makeChannels = OnMissingChannel.Create,
         AzureServiceBusSubscriptionConfiguration? subscriptionConfiguration = null,
diff --git a/src/Paramore.Brighter.MessagingGateway.Kafka/KafkaSubscription.cs b/src/Paramore.Brighter.MessagingGateway.Kafka/KafkaSubscription.cs
index c21c42c408..aff97d1e3b 100644
--- a/src/Paramore.Brighter.MessagingGateway.Kafka/KafkaSubscription.cs
+++ b/src/Paramore.Brighter.MessagingGateway.Kafka/KafkaSubscription.cs
@@ -148,7 +148,7 @@ public KafkaSubscription (
             TimeSpan? maxPollInterval = null, 
             TimeSpan? sweepUncommittedOffsetsInterval = null,
             IsolationLevel isolationLevel = IsolationLevel.ReadCommitted,
-            MessagePumpType messagePumpType = MessagePumpType.Proactor, 
+            MessagePumpType messagePumpType = MessagePumpType.Unknown, 
             int numOfPartitions = 1,
             short replicationFactor = 1,
             IAmAChannelFactory channelFactory = null, 
diff --git a/src/Paramore.Brighter.MessagingGateway.RMQ/RmqSubscription.cs b/src/Paramore.Brighter.MessagingGateway.RMQ/RmqSubscription.cs
index c596cad591..3e7f09d61f 100644
--- a/src/Paramore.Brighter.MessagingGateway.RMQ/RmqSubscription.cs
+++ b/src/Paramore.Brighter.MessagingGateway.RMQ/RmqSubscription.cs
@@ -100,7 +100,7 @@ public RmqSubscription(
             TimeSpan? requeueDelay = null, 
             int unacceptableMessageLimit = 0, 
             bool isDurable = false, 
-            MessagePumpType messagePumpType = MessagePumpType.Proactor, 
+            MessagePumpType messagePumpType = MessagePumpType.Unknown, 
             IAmAChannelFactory? channelFactory = null, 
             bool highAvailability = false, 
             ChannelName? deadLetterChannelName = null, 
diff --git a/src/Paramore.Brighter.MessagingGateway.Redis/RedisSubscription.cs b/src/Paramore.Brighter.MessagingGateway.Redis/RedisSubscription.cs
index 718178f0c1..2b0f7e386b 100644
--- a/src/Paramore.Brighter.MessagingGateway.Redis/RedisSubscription.cs
+++ b/src/Paramore.Brighter.MessagingGateway.Redis/RedisSubscription.cs
@@ -57,7 +57,7 @@ protected RedisSubscription(
             int requeueCount = -1, 
             TimeSpan? requeueDelay = null, 
             int unacceptableMessageLimit = 0, 
-            MessagePumpType messagePumpType = MessagePumpType.Proactor, 
+            MessagePumpType messagePumpType = MessagePumpType.Unknown, 
             IAmAChannelFactory? channelFactory = null, 
             OnMissingChannel makeChannels = OnMissingChannel.Create,
             TimeSpan? emptyChannelDelay = null,
diff --git a/src/Paramore.Brighter/MessagePumpType.cs b/src/Paramore.Brighter/MessagePumpType.cs
index 80bf074148..252cb0074f 100644
--- a/src/Paramore.Brighter/MessagePumpType.cs
+++ b/src/Paramore.Brighter/MessagePumpType.cs
@@ -2,6 +2,7 @@ namespace Paramore.Brighter;
 
 public enum MessagePumpType
 {
+    Unknown,
     Reactor,
     Proactor
 }
diff --git a/src/Paramore.Brighter/Subscription.cs b/src/Paramore.Brighter/Subscription.cs
index 4cb5ab50b3..9d7eb07e0c 100644
--- a/src/Paramore.Brighter/Subscription.cs
+++ b/src/Paramore.Brighter/Subscription.cs
@@ -153,12 +153,15 @@ public Subscription(
             int requeueCount = -1,
             TimeSpan? requeueDelay = null,
             int unacceptableMessageLimit = 0,
-            MessagePumpType messagePumpType = MessagePumpType.Proactor,
+            MessagePumpType messagePumpType = MessagePumpType.Unknown,
             IAmAChannelFactory? channelFactory = null,
             OnMissingChannel makeChannels = OnMissingChannel.Create,
             TimeSpan? emptyChannelDelay = null,
             TimeSpan? channelFailureDelay = null)
         {
+            if (messagePumpType == MessagePumpType.Unknown)
+                throw new ConfigurationException("You must set a message pump type: use Reactor for sync pipelines; use Proactor for async pipelines");
+            
             DataType = dataType;
             Name = name ?? new SubscriptionName(dataType.FullName!);
             ChannelName = channelName ?? new ChannelName(dataType.FullName!);
diff --git a/tests/Paramore.Brighter.InMemory.Tests/Consumer/When_an_inmemory_channelfactory_is_called.cs b/tests/Paramore.Brighter.InMemory.Tests/Consumer/When_an_inmemory_channelfactory_is_called.cs
index da2e306c9f..4fef77fac5 100644
--- a/tests/Paramore.Brighter.InMemory.Tests/Consumer/When_an_inmemory_channelfactory_is_called.cs
+++ b/tests/Paramore.Brighter.InMemory.Tests/Consumer/When_an_inmemory_channelfactory_is_called.cs
@@ -14,7 +14,7 @@ public void When_an_inmemory_channelfactory_is_called()
         var inMemoryChannelFactory = new InMemoryChannelFactory(internalBus, TimeProvider.System);
         
         //act
-        var channel = inMemoryChannelFactory.CreateSyncChannel(new Subscription(typeof(MyEvent)));
+        var channel = inMemoryChannelFactory.CreateSyncChannel(new Subscription(typeof(MyEvent), messagePumpType: MessagePumpType.Reactor));
         
         //assert
         Assert.NotNull(channel);