diff --git a/CHANGELOG.md b/CHANGELOG.md
index 31e40fc6..924c217e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,8 @@ Airbrake Ruby Changelog
   ([#25](https://github.com/airbrake/airbrake-ruby/pull/25))
 * Made sure that generated notices always have a backtrace
   ([#21](https://github.com/airbrake/airbrake-ruby/pull/21))
+* Made the asynchronous delivery mechanism more robust
+  ([#26](https://github.com/airbrake/airbrake-ruby/pull/26))
 
 ### [v1.0.2][v1.0.2] (January 3, 2016)
 
diff --git a/lib/airbrake-ruby/async_sender.rb b/lib/airbrake-ruby/async_sender.rb
index c79d2047..3e04d853 100644
--- a/lib/airbrake-ruby/async_sender.rb
+++ b/lib/airbrake-ruby/async_sender.rb
@@ -13,10 +13,7 @@ def initialize(config)
       @unsent = SizedQueue.new(config.queue_size)
       @sender = SyncSender.new(config)
       @closed = false
-      @workers = ThreadGroup.new
-
-      config.workers.times { @workers.add(spawn_worker) }
-      @workers.enclose
+      @workers = nil
     end
 
     ##
@@ -41,6 +38,11 @@ def close
         raise Airbrake::Error, 'attempted to close already closed sender'
       end
 
+      unless @workers
+        @closed = true
+        return
+      end
+
       unless @unsent.empty?
         msg = "#{LOG_LABEL} waiting to send #{@unsent.size} unsent notice(s)..."
         @config.logger.debug(msg + ' (Ctrl-C to abort)')
@@ -74,9 +76,22 @@ def closed?
     # @return [Boolean] true if an instance wasn't closed, but has no workers
     # @see https://goo.gl/oydz8h Example of at_exit that prevents exit
     def has_workers?
+      return false unless @workers
       !@closed && @workers.list.any?
     end
 
+    ##
+    # Spawns N workers (according to the config option) and creates a new
+    # enclosed ThreadGroup.
+    #
+    # @since v1.0.3
+    # @return [void]
+    def spawn_workers
+      @workers = ThreadGroup.new
+      @config.workers.times { @workers.add(spawn_worker) }
+      @workers.enclose
+    end
+
     private
 
     def spawn_worker
diff --git a/lib/airbrake-ruby/notifier.rb b/lib/airbrake-ruby/notifier.rb
index a1244fd2..e1dcecf5 100644
--- a/lib/airbrake-ruby/notifier.rb
+++ b/lib/airbrake-ruby/notifier.rb
@@ -33,6 +33,8 @@ def initialize(user_config)
       @filter_chain = FilterChain.new(@config)
       @async_sender = AsyncSender.new(@config)
       @sync_sender = SyncSender.new(@config)
+      @pid = nil
+      @workers_spawned = false
     end
 
     ##
@@ -42,6 +44,12 @@ def initialize(user_config)
     ##
     # @macro see_public_api_method
     def notify(exception, params = {})
+      if !@workers_spawned || @pid != Process.pid
+        @pid = Process.pid
+        @async_sender.spawn_workers
+        @workers_spawned = true
+      end
+
       send_notice(exception, params)
       nil
     end
@@ -127,15 +135,13 @@ def send_notice(exception, params, sender = default_sender)
     end
 
     def default_sender
-      if @async_sender.has_workers?
-        @async_sender
-      else
-        @config.logger.warn(
-          "#{LOG_LABEL} falling back to sync delivery because there are no " \
-          "running async workers"
-        )
-        @sync_sender
-      end
+      return @async_sender if @async_sender.has_workers?
+
+      @config.logger.warn(
+        "#{LOG_LABEL} falling back to sync delivery because there are no " \
+        "running async workers"
+      )
+      @sync_sender
     end
 
     def clean_backtrace
diff --git a/spec/async_sender_spec.rb b/spec/async_sender_spec.rb
index f4087902..ea479287 100644
--- a/spec/async_sender_spec.rb
+++ b/spec/async_sender_spec.rb
@@ -3,53 +3,6 @@
 RSpec.describe Airbrake::AsyncSender do
   before do
     stub_request(:post, /.*/).to_return(status: 201, body: '{}')
-    @sender = described_class.new(Airbrake::Config.new)
-    @workers = @sender.instance_variable_get(:@workers)
-  end
-
-  describe "#new" do
-    context "workers_count parameter" do
-      let(:new_workers) { 5 }
-      let(:config) { Airbrake::Config.new(workers: new_workers) }
-
-      it "spawns alive threads in an enclosed ThreadGroup" do
-        expect(@workers).to be_a(ThreadGroup)
-        expect(@workers.list).to all(be_alive)
-        expect(@workers).to be_enclosed
-      end
-
-      it "controls the number of spawned threads" do
-        expect(@workers.list.size).to eq(1)
-
-        sender = described_class.new(config)
-        workers = sender.instance_variable_get(:@workers)
-
-        expect(workers.list.size).to eq(new_workers)
-        sender.close
-      end
-    end
-
-    context "queue" do
-      before do
-        @stdout = StringIO.new
-      end
-
-      let(:notices) { 1000 }
-
-      let(:config) do
-        Airbrake::Config.new(logger: Logger.new(@stdout), workers: 3, queue_size: 10)
-      end
-
-      it "limits the size of the queue, but still sends all notices" do
-        sender = described_class.new(config)
-
-        notices.times { |i| sender.send(i) }
-        sender.close
-
-        log = @stdout.string.split("\n")
-        expect(log.grep(/\*\*Airbrake: \{\}/).size).to eq(notices)
-      end
-    end
   end
 
   describe "#close" do
@@ -57,14 +10,16 @@
       @stderr = StringIO.new
       config = Airbrake::Config.new(logger: Logger.new(@stderr))
       @sender = described_class.new(config)
-      @workers = @sender.instance_variable_get(:@workers).list
+      @sender.spawn_workers
     end
 
     context "when there are no unsent notices" do
       it "joins the spawned thread" do
-        expect(@workers).to all(be_alive)
+        workers = @sender.instance_variable_get(:@workers).list
+
+        expect(workers).to all(be_alive)
         @sender.close
-        expect(@workers).to all(be_stop)
+        expect(workers).to all(be_stop)
       end
     end
 
@@ -91,31 +46,92 @@
 
     context "when it was already closed" do
       it "doesn't increase the unsent queue size" do
-        @sender.close
+        begin
+          @sender.close
+        rescue Airbrake::Error
+          nil
+        end
+
         expect(@sender.instance_variable_get(:@unsent).size).to be_zero
+      end
 
+      it "raises error" do
+        @sender.close
+
+        expect(@sender).to be_closed
         expect { @sender.close }.
           to raise_error(Airbrake::Error, 'attempted to close already closed sender')
       end
     end
+
+    context "when workers were not spawned" do
+      it "correctly closes the notifier nevertheless" do
+        sender = described_class.new(Airbrake::Config.new)
+        sender.close
+
+        expect(sender).to be_closed
+      end
+    end
   end
 
   describe "#has_workers?" do
-    it "returns false when the sender is not closed, but has 0 workers" do
-      sender = described_class.new(Airbrake::Config.new)
-      expect(sender.has_workers?).to be_truthy
+    before do
+      @sender = described_class.new(Airbrake::Config.new)
+      @sender.spawn_workers
+      expect(@sender.has_workers?).to be_truthy
+    end
 
-      sender.instance_variable_get(:@workers).list.each(&:kill)
+    it "returns false when the sender is not closed, but has 0 workers" do
+      @sender.instance_variable_get(:@workers).list.each(&:kill)
       sleep 1
-      expect(sender.has_workers?).to be_falsey
+      expect(@sender.has_workers?).to be_falsey
     end
 
     it "returns false when the sender is closed" do
+      @sender.close
+      expect(@sender.has_workers?).to be_falsey
+    end
+  end
+
+  describe "#spawn_workers" do
+    it "spawns alive threads in an enclosed ThreadGroup" do
       sender = described_class.new(Airbrake::Config.new)
-      expect(sender.has_workers?).to be_truthy
+      sender.spawn_workers
+
+      workers = sender.instance_variable_get(:@workers)
+
+      expect(workers).to be_a(ThreadGroup)
+      expect(workers.list).to all(be_alive)
+      expect(workers).to be_enclosed
 
       sender.close
-      expect(sender.has_workers?).to be_falsey
+    end
+
+    it "spawns exactly config.workers workers" do
+      workers_count = 5
+      sender = described_class.new(Airbrake::Config.new(workers: workers_count))
+      sender.spawn_workers
+
+      workers = sender.instance_variable_get(:@workers)
+
+      expect(workers.list.size).to eq(workers_count)
+      sender.close
+    end
+
+    it "limits the size of the queue, but still sends all notices" do
+      stdout = StringIO.new
+      notices_count = 1000
+      config = Airbrake::Config.new(
+        logger: Logger.new(stdout), workers: 3, queue_size: 10
+      )
+      sender = described_class.new(config)
+      sender.spawn_workers
+
+      notices_count.times { |i| sender.send(i) }
+      sender.close
+
+      log = stdout.string.split("\n")
+      expect(log.grep(/\*\*Airbrake: \{\}/).size).to eq(notices_count)
     end
   end
 end
diff --git a/spec/notifier_spec.rb b/spec/notifier_spec.rb
index f6cc4ab9..211f6959 100644
--- a/spec/notifier_spec.rb
+++ b/spec/notifier_spec.rb
@@ -375,18 +375,53 @@ def to_json(*)
 
     it "falls back to synchronous delivery when the async sender is dead" do
       out = StringIO.new
+      notifier = described_class.new(airbrake_params.merge(logger: Logger.new(out)))
+      async_sender = notifier.instance_variable_get(:@async_sender)
 
-      airbrake = described_class.new(airbrake_params.merge(logger: Logger.new(out)))
-      airbrake.
-        instance_variable_get(:@async_sender).
-        instance_variable_get(:@workers).
-        list.
-        each(&:kill)
+      notifier.notify('bingo')
+      expect(async_sender.has_workers?).to be_truthy
 
+      async_sender.instance_variable_get(:@workers).list.each(&:kill)
       sleep 1
+      expect(async_sender.has_workers?).to be_falsey
 
-      expect(airbrake.notify('bingo')).to be_nil
+      notifier.notify('bango')
       expect(out.string).to match(/falling back to sync delivery/)
+
+      notifier.close
+    end
+
+    it "spawns workers on first invocation" do
+      out = StringIO.new
+      notifier = described_class.new(airbrake_params.merge(logger: Logger.new(out)))
+      async_sender = notifier.instance_variable_get(:@async_sender)
+
+      expect(async_sender.has_workers?).to be_falsey
+      notifier.notify('bingo')
+      sleep 1
+      expect(async_sender.has_workers?).to be_truthy
+
+      expect(out.string).not_to match(/falling back to sync delivery/)
+      notifier.close
+    end
+
+    it "respawns workers on fork()", skip: RUBY_ENGINE == 'jruby' do
+      notifier = described_class.new(airbrake_params)
+      async_sender = notifier.instance_variable_get(:@async_sender)
+
+      notifier.notify('bingo')
+      sleep 1
+      expect(async_sender.has_workers?).to be_truthy
+
+      pid = fork do
+        expect(async_sender.has_workers?).to be_falsey
+        notifier.notify('bango')
+        sleep 1
+        expect(async_sender.has_workers?).to be_truthy
+      end
+
+      Process.wait(pid)
+      notifier.close
     end
   end
 
@@ -671,25 +706,16 @@ def to_json(*)
   end
 
   describe "#close" do
-    shared_examples 'close' do |method|
+    context "when using #notify on a closed notifier" do
       it "raises error" do
-        @airbrake.close
-        expect { method.call(@airbrake) }.
+        notifier = described_class.new(airbrake_params)
+        notifier.close
+
+        expect { notifier.notify(AirbrakeTestError.new) }.
           to raise_error(Airbrake::Error, /closed Airbrake instance/)
       end
     end
 
-    context "when using #notify" do
-      include_examples 'close', proc { |a| a.notify(AirbrakeTestError.new) }
-    end
-
-    context "when using #send_notice" do
-      include_examples 'close', proc { |a|
-        notice = a.build_notice(AirbrakeTestError.new)
-        a.send_notice(notice)
-      }
-    end
-
     context "at program exit when it was closed manually" do
       it "doesn't raise error", skip: RUBY_ENGINE == 'jruby' do
         expect do