diff --git a/lib/rack/timeout/core.rb b/lib/rack/timeout/core.rb
index ae6247a..d07249c 100644
--- a/lib/rack/timeout/core.rb
+++ b/lib/rack/timeout/core.rb
@@ -133,7 +133,7 @@ def call(env)
       timeout = RT::Scheduler::Timeout.new do |app_thread|  # creates a timeout instance responsible for timing out the request. the given block runs if timed out
         register_state_change.call :timed_out
 
-        message = "Request "
+        message = +"Request "
         message << "waited #{info.ms(:wait)}, then " if info.wait
         message << "ran for longer than #{info.ms(:timeout)} "
         if term_on_timeout
diff --git a/lib/rack/timeout/logging-observer.rb b/lib/rack/timeout/logging-observer.rb
index 323d0d8..6740957 100644
--- a/lib/rack/timeout/logging-observer.rb
+++ b/lib/rack/timeout/logging-observer.rb
@@ -43,7 +43,7 @@ def log_state_change(env)
     info = env[::Rack::Timeout::ENV_INFO_KEY]
     level = STATE_LOG_LEVEL[info.state]
     logger(env).send(level) do
-      s  = "source=rack-timeout"
+      s  = +"source=rack-timeout"
       s << " id="      << info.id           if info.id
       s << " wait="    << info.ms(:wait)    if info.wait
       s << " timeout=" << info.ms(:timeout) if info.timeout