diff --git a/lib/message_bus_client/connection.rb b/lib/message_bus_client/connection.rb
index 4dc3dea..7b6cfd9 100644
--- a/lib/message_bus_client/connection.rb
+++ b/lib/message_bus_client/connection.rb
@@ -107,10 +107,10 @@ def headers
 
   # Gets the URI to poll the server with
   def server_endpoint
-    endpoint = "#{@base_url}/message-bus/#{@client_id}/poll"
+    endpoint = +"#{@base_url}/message-bus/#{@client_id}/poll"
     endpoint << '?dlp=t' unless self.class.long_polling
 
-    endpoint
+    endpoint.freeze
   end
 
   # Handles the response from the connection.
diff --git a/lib/message_bus_client/message_handler.rb b/lib/message_bus_client/message_handler.rb
index 6280007..63eb8b8 100644
--- a/lib/message_bus_client/message_handler.rb
+++ b/lib/message_bus_client/message_handler.rb
@@ -25,7 +25,7 @@ def initialize(base_url)
     @subscribed_channels.default_proc = proc do |hash, key|
       hash[key] = SubscribedChannel.new
     end
-    @payload = ''
+    @payload = +''
   end
 
   def subscribe(channel, &callback)