diff --git a/assets/scripts/app/models/artifact.coffee b/assets/scripts/app/models/artifact.coffee
index 26b87921..9177cfb3 100644
--- a/assets/scripts/app/models/artifact.coffee
+++ b/assets/scripts/app/models/artifact.coffee
@@ -1,4 +1,5 @@
 require 'travis/model'
+require 'travis/chunk_buffer'
 
 @Travis.Artifact = Em.Object.extend
   version: 1 # used to refresh log on requeue
diff --git a/assets/scripts/lib/travis/chunk_buffer.coffee b/assets/scripts/lib/travis/chunk_buffer.coffee
index 55379b48..83888df4 100644
--- a/assets/scripts/lib/travis/chunk_buffer.coffee
+++ b/assets/scripts/lib/travis/chunk_buffer.coffee
@@ -1,4 +1,4 @@
-Travis.ChunkBuffer = Em.ArrayProxy.extend
+Travis.ChunkBuffer = Em.ArrayProxy.extend Ember.MutableEnumerable,
   timeout: 15000
   start: 0
   next: 0
@@ -6,6 +6,8 @@ Travis.ChunkBuffer = Em.ArrayProxy.extend
   init: ->
     @_super.apply this, arguments
 
+    @set('next', @get('start'))
+
     if @get('content.length')
       @get('queue.content').pushObjects @get('content').toArray()
 
@@ -13,6 +15,15 @@ Travis.ChunkBuffer = Em.ArrayProxy.extend
     []
   ).property('content')
 
+  addObject: (obj) ->
+    @get('content').pushObject(obj)
+
+  removeObject: (obj) ->
+    @get('content').removeObject(obj)
+
+  replaceContent: (idx, amt, objects) ->
+    @get('content').replace(idx, amt, objects)
+
   queue: (->
     Em.ArrayProxy.create(Em.SortableMixin,
       content: []
@@ -35,9 +46,12 @@ Travis.ChunkBuffer = Em.ArrayProxy.extend
     next  = @get('next')
 
     arrangedContent = @get('arrangedContent')
+    toPush = []
 
     while queue.get('firstObject.number') == next
-      arrangedContent.pushObject queue.shiftObject().get('content')
+      toPush.pushObject queue.shiftObject().get('content')
       next += 1
 
+    arrangedContent.pushObjects toPush if toPush.length
+
     @set('next', next)
diff --git a/assets/scripts/spec/unit/chunk_buffer_spec.coffee b/assets/scripts/spec/unit/chunk_buffer_spec.coffee
index fca3cbac..56f98017 100644
--- a/assets/scripts/spec/unit/chunk_buffer_spec.coffee
+++ b/assets/scripts/spec/unit/chunk_buffer_spec.coffee
@@ -3,15 +3,14 @@ createChunk = (number, content) ->
 
 describe 'Travis.ChunkBuffer', ->
   it 'waits for parts to be in order before revealing them', ->
-    content = []
-    buffer = Travis.ChunkBuffer.create(content: content)
+    buffer = Travis.ChunkBuffer.create(content: [])
 
-    content.pushObject createChunk(2, "baz")
-    content.pushObject createChunk(1, "bar")
+    buffer.pushObject createChunk(2, "baz")
+    buffer.pushObject createChunk(1, "bar")
 
     expect(buffer.get('length')).toEqual(0)
 
-    content.pushObject createChunk(0, "foo")
+    buffer.pushObject createChunk(0, "foo")
 
     expect(buffer.get('length')).toEqual(3)
 
@@ -20,14 +19,13 @@ describe 'Travis.ChunkBuffer', ->
   it 'ignores a part if it fails to be delivered within timeout', ->
     expect 4
 
-    content = []
-    buffer = Travis.ChunkBuffer.create(content: content, timeout: 10)
+    buffer = Travis.ChunkBuffer.create(content: [], timeout: 10)
 
-    content.pushObject createChunk(2, "baz")
+    buffer.pushObject createChunk(2, "baz")
 
     expect(buffer.get('length')).toEqual(0)
 
-    content.pushObject createChunk(0, "foo")
+    buffer.pushObject createChunk(0, "foo")
 
     expect(buffer.get('length')).toEqual(1)
 
@@ -44,9 +42,39 @@ describe 'Travis.ChunkBuffer', ->
 
     expect(buffer.get('length')).toEqual(0)
 
-    content.pushObject createChunk(0, "foo")
+    buffer.pushObject createChunk(0, "foo")
 
     expect(buffer.get('length')).toEqual(2)
     expect(buffer.toArray()).toEqual(['foo', 'bar'])
 
+  it 'fires array observers properly', ->
+    changes = []
+    buffer = Travis.ChunkBuffer.create(content: [])
 
+    observer = Em.Object.extend(
+      init: ->
+        @_super.apply this, arguments
+
+        @get('content').addArrayObserver this,
+          willChange: 'arrayWillChange',
+          didChange: 'arrayDidChange'
+
+      arrayWillChange: (->)
+      arrayDidChange: (array, index, removedCount, addedCount) ->
+        changes.pushObject([index, addedCount])
+    ).create(content: buffer)
+
+    buffer.pushObject createChunk(1, "baz")
+
+    expect(buffer.get('length')).toEqual(0)
+    expect(changes.length).toEqual(0)
+
+    buffer.pushObject createChunk(0, "foo")
+
+    expect(buffer.get('length')).toEqual(2)
+    expect(changes.length).toEqual(1)
+    expect(changes[0]).toEqual([0, 2])
+
+  it 'sets next to start if start is given at init', ->
+    buffer = Travis.ChunkBuffer.create(content: [], start: 5)
+    expect(buffer.get('next')).toEqual(5)