diff --git a/lib/puma/cli.rb b/lib/puma/cli.rb
index 0fadffdd..a8c91a33 100644
--- a/lib/puma/cli.rb
+++ b/lib/puma/cli.rb
@@ -491,7 +491,7 @@ module Puma
       set_rack_environment
 
       if clustered?
-        @events = PidEvents.new STDOUT, STDERR
+        @events.formatter = Events::PidFormatter.new
         @options[:logger] = @events
 
         @runner = Cluster.new(self)
diff --git a/lib/puma/events.rb b/lib/puma/events.rb
index 2c3325a8..c90ebaae 100644
--- a/lib/puma/events.rb
+++ b/lib/puma/events.rb
@@ -8,12 +8,24 @@ module Puma
   # The methods available are the events that the Server fires.
   #
   class Events
+    class DefaultFormatter
+      def call(str)
+        str
+      end
+    end
+
+    class PidFormatter
+      def call(str)
+        "[#{$$}] #{str}"
+      end
+    end
 
     include Const
 
     # Create an Events object that prints to +stdout+ and +stderr+.
     #
     def initialize(stdout, stderr)
+      @formatter = DefaultFormatter.new
       @stdout = stdout
       @stderr = stderr
 
@@ -28,6 +40,7 @@ module Puma
     end
 
     attr_reader :stdout, :stderr
+    attr_accessor :formatter
 
     # Fire callbacks for the named hook
     #
@@ -52,11 +65,11 @@ module Puma
     # Write +str+ to +@stdout+
     #
     def log(str)
-      @stdout.puts str
+      @stdout.puts format(str)
     end
 
     def write(str)
-      @stdout.write str
+      @stdout.write format(str)
     end
 
     def debug(str)
@@ -66,10 +79,14 @@ module Puma
     # Write +str+ to +@stderr+
     #
     def error(str)
-      @stderr.puts "ERROR: #{str}"
+      @stderr.puts format("ERROR: #{str}")
       exit 1
     end
 
+    def format(str)
+      formatter.call(str)
+    end
+
     # An HTTP parse error has occured.
     # +server+ is the Server object, +env+ the request, and +error+ a
     # parsing exception.
@@ -113,18 +130,4 @@ module Puma
       Events.new $stdout, $stderr
     end
   end
-
-  class PidEvents < Events
-    def log(str)
-      super "[#{$$}] #{str}"
-    end
-
-    def write(str)
-      super "[#{$$}] #{str}"
-    end
-
-    def error(str)
-      super "[#{$$}] #{str}"
-    end
-  end
 end