diff --git a/lib/mqtt/client.rb b/lib/mqtt/client.rb
index e46d14c..f5f3b9f 100644
--- a/lib/mqtt/client.rb
+++ b/lib/mqtt/client.rb
@@ -332,14 +332,11 @@ def publish(topic, payload = '', retain = false, qos = 0)
         :payload => payload
       )
 
-      # Send the packet
-      res = send_packet(packet)
-
-      return if qos.zero?
+      queue = qos.zero? ? nil : wait_for_puback(packet.id)
 
-      queue = Queue.new
+      res = send_packet(packet)
 
-      wait_for_puback packet.id, queue
+      return unless queue
 
       deadline = current_time + @ack_timeout
 
@@ -488,9 +485,9 @@ def receive_packet
       Thread.current[:parent].raise(exp)
     end
 
-    def wait_for_puback(id, queue)
+    def wait_for_puback(id)
       @pubacks_semaphore.synchronize do
-        @pubacks[id] = queue
+        @pubacks[id] = Queue.new
       end
     end
 
@@ -502,7 +499,7 @@ def handle_packet(packet)
         @last_ping_response = current_time
       elsif packet.class == MQTT::Packet::Puback
         @pubacks_semaphore.synchronize do
-          @pubacks[packet.id] << packet
+          @pubacks[packet.id] << packet if @pubacks[packet.id]
         end
       end
       # Ignore all other packets
diff --git a/spec/mqtt_client_spec.rb b/spec/mqtt_client_spec.rb
index c09af57..28a701f 100644
--- a/spec/mqtt_client_spec.rb
+++ b/spec/mqtt_client_spec.rb
@@ -641,11 +641,11 @@ def inject_puback(packet)
         @injected_pubacks[packet.id] = packet
       end
 
-      def wait_for_puback(id, queue)
+      def wait_for_puback(id)
         packet = @injected_pubacks.fetch(id) {
           return super
         }
-        queue << packet
+        Queue.new << packet
       end
     end
 
@@ -745,6 +745,20 @@ def wait_for_puback(id, queue)
       expect(client).to receive(:send_packet) { |packet| expect(packet.id).to eq(2) }
       client.publish "topic", "message", false, 1
     end
+
+    it "does not crash when receiving a PUBACK for a packet it never sent" do
+      expect { client.send(:handle_packet, MQTT::Packet::Puback.new(:id => 666)) }.to_not raise_error
+    end
+
+    it "does not crash with QoS 1 when the broker sends the PUBACK instantly" do
+      allow(client).to receive(:send_packet).and_wrap_original do |send_packet, packet, *args, **kwargs, &block|
+        send_packet.call(packet, *args, **kwargs, &block).tap do
+          client.send(:handle_packet, MQTT::Packet::Puback.new(:id => packet.id))
+        end
+      end
+
+      expect { client.publish("topic", "message", false, 1) }.to_not raise_error
+    end
   end
 
   describe "when calling the 'subscribe' method" do