diff --git a/lib/segment/analytics/defaults.rb b/lib/segment/analytics/defaults.rb
index 18cf861..8562346 100644
--- a/lib/segment/analytics/defaults.rb
+++ b/lib/segment/analytics/defaults.rb
@@ -13,7 +13,6 @@ module Request
       end
 
       module Queue
-        BATCH_SIZE = 100
         MAX_SIZE = 10000
       end
 
@@ -21,6 +20,11 @@ module Message
         MAX_BYTES = 32768 # 32Kb
       end
 
+      module MessageBatch
+        MAX_BYTES = 512_000 # 500Kb
+        MAX_SIZE = 100
+      end
+
       module BackoffPolicy
         MIN_TIMEOUT_MS = 100
         MAX_TIMEOUT_MS = 10000
diff --git a/lib/segment/analytics/message.rb b/lib/segment/analytics/message.rb
index b11b121..e00a74d 100644
--- a/lib/segment/analytics/message.rb
+++ b/lib/segment/analytics/message.rb
@@ -9,7 +9,11 @@ def initialize(hash)
       end
 
       def too_big?
-        to_json.bytesize > Defaults::Message::MAX_BYTES
+        json_size > Defaults::Message::MAX_BYTES
+      end
+
+      def json_size
+        to_json.bytesize
       end
 
       # Since the hash is expected to not be modified (set at initialization),
diff --git a/lib/segment/analytics/message_batch.rb b/lib/segment/analytics/message_batch.rb
index 0cf1dc4..bc44971 100644
--- a/lib/segment/analytics/message_batch.rb
+++ b/lib/segment/analytics/message_batch.rb
@@ -6,9 +6,12 @@ class Analytics
     class MessageBatch
       extend Forwardable
       include Segment::Analytics::Logging
+      include Segment::Analytics::Defaults::MessageBatch
 
-      def initialize
+      def initialize(max_message_count)
         @messages = []
+        @max_message_count = max_message_count
+        @json_size = 0
       end
 
       def <<(message)
@@ -16,13 +19,40 @@ def <<(message)
           logger.error('a message exceeded the maximum allowed size')
         else
           @messages << message
+          @json_size += message.json_size + 1 # One byte for the comma
         end
       end
 
+      def full?
+        item_count_exhausted? || size_exhausted?
+      end
+
+      def clear
+        @messages.clear
+        @json_size = 0
+      end
+
       def_delegators :@messages, :to_json
-      def_delegators :@messages, :clear
       def_delegators :@messages, :empty?
       def_delegators :@messages, :length
+
+      private
+
+      def item_count_exhausted?
+        @messages.length >= @max_message_count
+      end
+
+      # We consider the max size here as just enough to leave room for one more
+      # message of the largest size possible. This is a shortcut that allows us
+      # to use a native Ruby `Queue` that doesn't allow peeking. The tradeoff
+      # here is that we might fit in less messages than possible into a batch.
+      #
+      # The alternative is to use our own `Queue` implementation that allows
+      # peeking, and to consider the next message size when calculating whether
+      # the message can be accomodated in this batch.
+      def size_exhausted?
+        @json_size >= (MAX_BYTES - Defaults::Message::MAX_BYTES)
+      end
     end
   end
 end
diff --git a/lib/segment/analytics/worker.rb b/lib/segment/analytics/worker.rb
index a5fb638..f1c7ef4 100644
--- a/lib/segment/analytics/worker.rb
+++ b/lib/segment/analytics/worker.rb
@@ -25,9 +25,9 @@ def initialize(queue, write_key, options = {})
         symbolize_keys! options
         @queue = queue
         @write_key = write_key
-        @batch_size = options[:batch_size] || Queue::BATCH_SIZE
         @on_error = options[:on_error] || proc { |status, error| }
-        @batch = MessageBatch.new
+        batch_size = options[:batch_size] || Defaults::MessageBatch::MAX_SIZE
+        @batch = MessageBatch.new(batch_size)
         @lock = Mutex.new
         @request = Request.new
       end
@@ -39,7 +39,7 @@ def run
           return if @queue.empty?
 
           @lock.synchronize do
-            until @batch.length >= @batch_size || @queue.empty?
+            until @batch.full? || @queue.empty?
               @batch << Message.new(@queue.pop)
             end
           end
diff --git a/spec/helpers/runscope_client.rb b/spec/helpers/runscope_client.rb
index 7d0e7f8..a68be26 100644
--- a/spec/helpers/runscope_client.rb
+++ b/spec/helpers/runscope_client.rb
@@ -9,7 +9,7 @@ def initialize(api_token)
 
   def requests(bucket_key)
     with_retries(3) do
-      response = @conn.get("/buckets/#{bucket_key}/messages", count: 10)
+      response = @conn.get("/buckets/#{bucket_key}/messages", count: 20)
 
       raise "Runscope error. #{response.body}" unless response.status == 200
 
diff --git a/spec/segment/analytics/message_batch_spec.rb b/spec/segment/analytics/message_batch_spec.rb
index e50f4d0..6e014c8 100644
--- a/spec/segment/analytics/message_batch_spec.rb
+++ b/spec/segment/analytics/message_batch_spec.rb
@@ -3,16 +3,16 @@
 module Segment
   class Analytics
     describe MessageBatch do
-      describe '#<<' do
-        subject { described_class.new }
+      subject { described_class.new(100) }
 
+      describe '#<<' do
         it 'appends messages' do
           subject << Message.new('a' => 'b')
           expect(subject.length).to eq(1)
         end
 
         it 'rejects messages that exceed the maximum allowed size' do
-          max_bytes = Segment::Analytics::Defaults::Message::MAX_BYTES
+          max_bytes = Defaults::Message::MAX_BYTES
           hash = { 'a' => 'b' * max_bytes }
           message = Message.new(hash)
 
@@ -20,6 +20,30 @@ class Analytics
           expect(subject.length).to eq(0)
         end
       end
+
+      describe '#full?' do
+        it 'returns true once item count is exceeded' do
+          99.times { subject << Message.new(a: 'b') }
+          expect(subject.full?).to be(false)
+
+          subject << Message.new(a: 'b')
+          expect(subject.full?).to be(true)
+        end
+
+        it 'returns true once max size is almost exceeded' do
+          message = Message.new(a: 'b' * (Defaults::Message::MAX_BYTES - 10))
+
+          # Each message is under the individual limit
+          expect(message.json_size).to be < Defaults::Message::MAX_BYTES
+
+          # Size of the batch is over the limit
+          expect(50 * message.json_size).to be > Defaults::MessageBatch::MAX_BYTES
+
+          expect(subject.full?).to be(false)
+          50.times { subject << message }
+          expect(subject.full?).to be(true)
+        end
+      end
     end
   end
 end
diff --git a/spec/segment/analytics/worker_spec.rb b/spec/segment/analytics/worker_spec.rb
index 3abd4d8..e66db64 100644
--- a/spec/segment/analytics/worker_spec.rb
+++ b/spec/segment/analytics/worker_spec.rb
@@ -6,8 +6,11 @@ class Analytics
       describe '#init' do
         it 'accepts string keys' do
           queue = Queue.new
-          worker = Segment::Analytics::Worker.new(queue, 'secret', 'batch_size' => 100)
-          expect(worker.instance_variable_get(:@batch_size)).to eq(100)
+          worker = Segment::Analytics::Worker.new(queue,
+                                                  'secret',
+                                                  'batch_size' => 100)
+          batch = worker.instance_variable_get(:@batch)
+          expect(batch.instance_variable_get(:@max_message_count)).to eq(100)
         end
       end
 
@@ -35,8 +38,11 @@ class Analytics
           end.to_not raise_error
         end
 
-        it 'executes the error handler, before the request phase ends, if the request is invalid' do
-          Segment::Analytics::Request.any_instance.stub(:post).and_return(Segment::Analytics::Response.new(400, 'Some error'))
+        it 'executes the error handler if the request is invalid' do
+          Segment::Analytics::Request
+            .any_instance
+            .stub(:post)
+            .and_return(Segment::Analytics::Response.new(400, 'Some error'))
 
           status = error = nil
           on_error = proc do |yielded_status, yielded_error|
@@ -46,9 +52,10 @@ class Analytics
 
           queue = Queue.new
           queue << {}
-          worker = Segment::Analytics::Worker.new queue, 'secret', :on_error => on_error
+          worker = described_class.new(queue, 'secret', :on_error => on_error)
 
-          # This is to ensure that Client#flush doesn't finish before calling the error handler.
+          # This is to ensure that Client#flush doesn't finish before calling
+          # the error handler.
           Thread.new { worker.run }
           sleep 0.1 # First give thread time to spin-up.
           sleep 0.01 while worker.is_requesting?
@@ -69,7 +76,9 @@ class Analytics
 
           queue = Queue.new
           queue << Requested::TRACK
-          worker = Segment::Analytics::Worker.new queue, 'testsecret', :on_error => on_error
+          worker = described_class.new(queue,
+                                       'testsecret',
+                                       :on_error => on_error)
           worker.run
 
           expect(queue).to be_empty
@@ -89,12 +98,11 @@ class Analytics
           queue << Requested::TRACK
           worker = Segment::Analytics::Worker.new(queue, 'testsecret')
 
-          Thread.new do
-            worker.run
-            expect(worker.is_requesting?).to eq(false)
-          end
-
+          worker_thread = Thread.new { worker.run }
           eventually { expect(worker.is_requesting?).to eq(true) }
+
+          worker_thread.join
+          expect(worker.is_requesting?).to eq(false)
         end
       end
     end