diff --git a/akka-actor/src/main/scala/akka/dispatch/Mailbox.scala b/akka-actor/src/main/scala/akka/dispatch/Mailbox.scala
index 676c33b48c..58a498b948 100644
--- a/akka-actor/src/main/scala/akka/dispatch/Mailbox.scala
+++ b/akka-actor/src/main/scala/akka/dispatch/Mailbox.scala
@@ -292,6 +292,12 @@ trait DefaultSystemMessageQueue { self: Mailbox ⇒
   def hasSystemMessages: Boolean = systemQueueGet ne null
 }
 
+trait QueueBasedMessageQueue extends MessageQueue {
+  def queue: Queue[Envelope]
+  final def numberOfMessages = queue.size
+  final def hasMessages = !queue.isEmpty
+}
+
 trait UnboundedMessageQueueSemantics extends QueueBasedMessageQueue {
   final def enqueue(receiver: ActorRef, handle: Envelope): Unit = queue add handle
   final def dequeue(): Envelope = queue.poll()
@@ -301,21 +307,20 @@ trait BoundedMessageQueueSemantics extends QueueBasedMessageQueue {
   def pushTimeOut: Duration
   override def queue: BlockingQueue[Envelope]
 
-  final def enqueue(receiver: ActorRef, handle: Envelope) {
-    if (pushTimeOut.length > 0) {
+  final def enqueue(receiver: ActorRef, handle: Envelope): Unit =
+    if (pushTimeOut.length > 0)
       queue.offer(handle, pushTimeOut.length, pushTimeOut.unit) || {
         throw new MessageQueueAppendFailedException("Couldn't enqueue message " + handle + " to " + receiver)
       }
-    } else queue put handle
-  }
+    else queue put handle
 
   final def dequeue(): Envelope = queue.poll()
 }
 
-trait QueueBasedMessageQueue extends MessageQueue {
-  def queue: Queue[Envelope]
-  final def numberOfMessages = queue.size
-  final def hasMessages = !queue.isEmpty
+trait DequeBasedMessageQueue extends QueueBasedMessageQueue {
+  def queue: Deque[Envelope]
+  def enqueueFirst(receiver: ActorRef, handle: Envelope): Unit
+  def enqueueAllFirst(receiver: ActorRef, handleIterator: Iterator[Envelope], size: Int): Unit
 }
 
 trait UnboundedDequeBasedMessageQueueSemantics extends DequeBasedMessageQueue {
@@ -323,7 +328,7 @@ trait UnboundedDequeBasedMessageQueueSemantics extends DequeBasedMessageQueue {
 
   final def enqueueFirst(receiver: ActorRef, handle: Envelope): Unit = queue addFirst handle
 
-  final def enqueueAllFirst(receiver: ActorRef, handleIterator: Iterator[Envelope], size: Int) =
+  final def enqueueAllFirst(receiver: ActorRef, handleIterator: Iterator[Envelope], size: Int): Unit =
     handleIterator foreach { enqueueFirst(receiver, _) }
 
   final def dequeue(): Envelope = queue.poll()
@@ -333,37 +338,28 @@ trait BoundedDequeBasedMessageQueueSemantics extends DequeBasedMessageQueue {
   def pushTimeOut: Duration
   override def queue: BlockingDeque[Envelope]
 
-  final def enqueue(receiver: ActorRef, handle: Envelope) {
-    if (pushTimeOut.length > 0) {
+  final def enqueue(receiver: ActorRef, handle: Envelope): Unit =
+    if (pushTimeOut.length > 0)
       queue.offer(handle, pushTimeOut.length, pushTimeOut.unit) || {
         throw new MessageQueueAppendFailedException("Couldn't enqueue message " + handle + " to " + receiver)
       }
-    } else queue put handle
-  }
+    else queue put handle
 
-  final def enqueueFirst(receiver: ActorRef, handle: Envelope) {
-    if (pushTimeOut.length > 0) {
+  final def enqueueFirst(receiver: ActorRef, handle: Envelope): Unit =
+    if (pushTimeOut.length > 0)
       queue.offerFirst(handle, pushTimeOut.length, pushTimeOut.unit) || {
         throw new MessageQueueAppendFailedException("Couldn't enqueue message " + handle + " to " + receiver)
       }
-    } else queue putFirst handle
-  }
+    else queue putFirst handle
 
-  final def enqueueAllFirst(receiver: ActorRef, handleIterator: Iterator[Envelope], size: Int) {
-    if (queue.asInstanceOf[BlockingQueue[Envelope]].remainingCapacity >= size) {
+  final def enqueueAllFirst(receiver: ActorRef, handleIterator: Iterator[Envelope], size: Int): Unit =
+    if (queue.asInstanceOf[BlockingQueue[Envelope]].remainingCapacity >= size)
       handleIterator foreach { enqueueFirst(receiver, _) }
-    } else throw new MessageQueueAppendFailedException("Couldn't enqueue stash to " + receiver)
-  }
+    else throw new MessageQueueAppendFailedException("Couldn't enqueue stash to " + receiver)
 
   final def dequeue(): Envelope = queue.poll()
 }
 
-trait DequeBasedMessageQueue extends QueueBasedMessageQueue {
-  def queue: Deque[Envelope]
-  def enqueueFirst(receiver: ActorRef, handle: Envelope): Unit
-  def enqueueAllFirst(receiver: ActorRef, handleIterator: Iterator[Envelope], size: Int): Unit
-}
-
 /**
  * Mailbox configuration.
  */