diff --git a/Library/Homebrew/build.rb b/Library/Homebrew/build.rb
index 34903c9aa3..14209dd81a 100644
--- a/Library/Homebrew/build.rb
+++ b/Library/Homebrew/build.rb
@@ -8,7 +8,7 @@ require "build_options"
 require "cxxstdlib"
 require "keg"
 require "extend/ENV"
-require "debrew" if ARGV.debug?
+require "debrew"
 require "fcntl"
 
 class Build
@@ -109,6 +109,11 @@ class Build
       end
     end
 
+    if ARGV.debug?
+      formula.extend(Debrew::Formula)
+      formula.resources.each { |r| r.extend(Debrew::Resource) }
+    end
+
     formula.brew do
       if ARGV.flag? '--git'
         system "git", "init"
@@ -129,17 +134,7 @@ class Build
       else
         formula.prefix.mkpath
 
-        formula.resources.each { |r| r.extend(ResourceDebugger) } if ARGV.debug?
-
-        begin
-          formula.install
-        rescue Exception => e
-          if ARGV.debug?
-            debrew(e, formula)
-          else
-            raise
-          end
-        end
+        formula.install
 
         stdlibs = detect_stdlibs
         Tab.create(formula, ENV.compiler, stdlibs.first, formula.build).write
@@ -190,7 +185,6 @@ begin
   build   = Build.new(formula, options)
   build.install
 rescue Exception => e
-  e.continuation = nil if ARGV.debug?
   Marshal.dump(e, error_pipe)
   error_pipe.close
   exit! 1
diff --git a/Library/Homebrew/debrew.rb b/Library/Homebrew/debrew.rb
index e8df1aeec7..fbddadbd53 100644
--- a/Library/Homebrew/debrew.rb
+++ b/Library/Homebrew/debrew.rb
@@ -1,75 +1,148 @@
-require 'debrew/menu'
-require 'debrew/raise_plus'
-require 'set'
+require "mutex_m"
+require "debrew/irb" unless ENV["HOMEBREW_NO_READLINE"]
 
-unless ENV['HOMEBREW_NO_READLINE']
-  begin
-    require 'rubygems'
-    require 'ruby-debug'
-  rescue LoadError
+module Debrew
+  extend Mutex_m
+
+  Ignorable = Module.new
+
+  module Raise
+    def raise(*)
+      super
+    rescue Exception => e
+      e.extend(Ignorable)
+      super(e) unless Debrew.debug(e) == :ignore
+    end
+
+    alias_method :fail, :raise
   end
 
-  require 'debrew/irb'
-end
+  module Formula
+    def install
+      Debrew.debrew { super }
+    end
+  end
 
-class Object
-  include RaisePlus
-end
+  module Resource
+    def unpack(target=nil)
+      return super if target
+      super do
+        begin
+          yield self
+        rescue Exception => e
+          Debrew.debug(e)
+        end
+      end
+    end
+  end
 
-module ResourceDebugger
-  def stage(target=nil, &block)
-    return super if target
+  class Menu
+    Entry = Struct.new(:name, :action)
 
-    super do
-      begin
-        block.call(self)
-      rescue Exception => e
-        if ARGV.debug?
-          debrew e
+    attr_accessor :prompt, :entries
+
+    def initialize
+      @entries = []
+    end
+
+    def choice(name, &action)
+      entries << Entry.new(name.to_s, action)
+    end
+
+    def self.choose
+      menu = new
+      yield menu
+
+      choice = nil
+      while choice.nil?
+        menu.entries.each_with_index { |e, i| puts "#{i+1}. #{e.name}" }
+        print menu.prompt unless menu.prompt.nil?
+
+        input = $stdin.gets.chomp
+
+        i = input.to_i
+        if i > 0
+          choice = menu.entries[i-1]
         else
-          raise
+          possible = menu.entries.find_all { |e| e.name.start_with?(input) }
+
+          case possible.size
+          when 0 then puts "No such option"
+          when 1 then choice = possible.first
+          else puts "Multiple options match: #{possible.map(&:name).join(" ")}"
+          end
         end
       end
+
+      choice[:action].call
+    end
+  end
+
+  class << self
+    alias_method :original_raise, :raise
+  end
+
+  @active = false
+  @debugged_exceptions = Set.new
+
+  def self.active?
+    @active
+  end
+
+  def self.debugged_exceptions
+    @debugged_exceptions
+  end
+
+  def self.debrew
+    @active = true
+    Object.send(:include, Raise)
+
+    begin
+      yield
+    rescue Exception => e
+      debug(e)
+    ensure
+      @active = false
+    end
+  end
+
+  def self.debug(e)
+    original_raise(e) unless active? &&
+                             debugged_exceptions.add?(e) &&
+                             try_lock
+
+    begin
+      puts "#{e.backtrace.first}"
+      puts "#{Tty.red}#{e.class.name}#{Tty.reset}: #{e}"
+
+      loop do
+        Menu.choose do |menu|
+          menu.prompt = "Choose an action: "
+
+          menu.choice(:raise) { original_raise(e) }
+          menu.choice(:ignore) { return :ignore } if Ignorable === e
+          menu.choice(:backtrace) { puts e.backtrace }
+
+          menu.choice(:irb) do
+            puts "When you exit this IRB session, execution will continue."
+            set_trace_func proc { |event, _, _, id, binding, klass|
+              if klass == Raise && id == :raise && event == "return"
+                set_trace_func(nil)
+                synchronize { IRB.start_within(binding) }
+              end
+            }
+
+            return :ignore
+          end if Object.const_defined?(:IRB) && Ignorable === e
+
+          menu.choice(:shell) do
+            puts "When you exit this shell, you will return to the menu."
+            interactive_shell
+          end
+        end
+      end
+    ensure
+      unlock
     end
   end
 end
-
-$debugged_exceptions = Set.new
-
-def debrew(exception, formula=nil)
-  raise exception unless $debugged_exceptions.add?(exception)
-
-  puts "#{exception.backtrace.first}"
-  puts "#{Tty.red}#{exception.class.name}#{Tty.reset}: #{exception}"
-
-  begin
-    again = false
-    choose do |menu|
-      menu.prompt = "Choose an action: "
-      menu.choice(:raise) { original_raise exception }
-      menu.choice(:ignore) { exception.restart } if exception.continuation
-      menu.choice(:backtrace) { puts exception.backtrace; again = true }
-      menu.choice(:debug) do
-        puts "When you exit the debugger, execution will continue."
-        exception.restart { debugger }
-      end if Object.const_defined?(:Debugger)
-      menu.choice(:irb) do
-        puts "When you exit this IRB session, execution will continue."
-        exception.restart do
-          # we need to capture the binding after returning from raise
-          set_trace_func proc { |event, file, line, id, binding, classname|
-            if event == 'return'
-              set_trace_func nil
-              IRB.start_within(binding)
-            end
-          }
-        end
-      end if Object.const_defined?(:IRB) && exception.continuation
-      menu.choice(:shell) do
-        puts "When you exit this shell, you will return to the menu."
-        interactive_shell formula
-        again=true
-      end
-    end
-  end while again
-end
diff --git a/Library/Homebrew/debrew/exception.rb b/Library/Homebrew/debrew/exception.rb
deleted file mode 100644
index da8e56dae0..0000000000
--- a/Library/Homebrew/debrew/exception.rb
+++ /dev/null
@@ -1,7 +0,0 @@
-class Exception
-  attr_accessor :continuation
-
-  def restart(&block)
-    continuation.call block
-  end
-end
diff --git a/Library/Homebrew/debrew/menu.rb b/Library/Homebrew/debrew/menu.rb
deleted file mode 100644
index c59c500b8e..0000000000
--- a/Library/Homebrew/debrew/menu.rb
+++ /dev/null
@@ -1,39 +0,0 @@
-class Menu
-  attr_accessor :prompt
-  attr_accessor :entries
-
-  def initialize
-    @entries = []
-  end
-
-  def choice(name, &action)
-    entries << { :name => name, :action => action }
-  end
-end
-
-def choose
-  menu = Menu.new
-  yield menu
-
-  choice = nil
-  while choice.nil?
-    menu.entries.each_with_index do |entry, i|
-      puts "#{i+1}. #{entry[:name]}"
-    end
-    print menu.prompt unless menu.prompt.nil?
-    reply = $stdin.gets.chomp
-
-    i = reply.to_i
-    if i > 0
-      choice = menu.entries[i-1]
-    else
-      possible = menu.entries.find_all {|e| e[:name].to_s.start_with? reply }
-      case possible.size
-        when 0 then puts "No such option"
-        when 1 then choice = possible.first
-        else puts "Multiple options match: #{possible.map{|e| e[:name]}.join(' ')}"
-      end
-    end
-  end
-  choice[:action].call
-end
diff --git a/Library/Homebrew/debrew/raise_plus.rb b/Library/Homebrew/debrew/raise_plus.rb
deleted file mode 100644
index 29bf4106a1..0000000000
--- a/Library/Homebrew/debrew/raise_plus.rb
+++ /dev/null
@@ -1,46 +0,0 @@
-require 'continuation' if RUBY_VERSION.to_f >= 1.9
-
-class Exception
-  attr_accessor :continuation
-
-  def restart(&block)
-    continuation.call block
-  end
-end
-
-module RaisePlus
-  alias :original_raise :raise
-
-  private
-
-  def raise(*args)
-    exception = case
-                when args.size == 0
-                  $!.nil? ? RuntimeError.exception : $!
-                when args.size == 1 && args[0].is_a?(String)
-                  RuntimeError.exception(args[0])
-                when args.size == 2 && args[0].is_a?(Exception)
-                  args[0].exception(args[1])
-                when args[0].is_a?(Class) && args[0].ancestors.include?(Exception)
-                  args[0].exception(args[1])
-                else
-                  args[0]
-                end
-
-    # passing something other than a String or Exception is illegal, but if someone does it anyway,
-    # that object won't have backtrace or continuation methods. in that case, let's pass it on to
-    # the original raise, which will reject it
-    return super exception unless exception.is_a?(Exception)
-
-    # keep original backtrace if reraising
-    exception.set_backtrace(args.size >= 3 ? args[2] : caller) if exception.backtrace.nil?
-
-    blk = callcc do |cc|
-      exception.continuation = cc
-      super exception
-    end
-    blk.call unless blk.nil?
-  end
-
-  alias :fail :raise
-end
diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index bb76a69cd7..d457da4303 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -12,6 +12,7 @@ require 'formula_cellar_checks'
 require 'install_renamed'
 require 'cmd/tap'
 require 'hooks/bottles'
+require 'debrew'
 
 class FormulaInstaller
   include FormulaCellarChecks
diff --git a/Library/Homebrew/test/test_raise_plus.rb b/Library/Homebrew/test/test_raise_plus.rb
deleted file mode 100644
index 109c6e7377..0000000000
--- a/Library/Homebrew/test/test_raise_plus.rb
+++ /dev/null
@@ -1,45 +0,0 @@
-require 'testing_env'
-require 'debrew/raise_plus'
-
-class RaisePlusTests < Homebrew::TestCase
-  include RaisePlus
-
-  def test_raises_runtime_error_when_no_args
-    assert_raises(RuntimeError) { raise }
-  end
-
-  def test_raises_runtime_error_with_string_arg
-    raise "foo"
-  rescue Exception => e
-    assert_kind_of RuntimeError, e
-    assert_equal "foo", e.to_s
-  end
-
-  def test_raises_given_exception_with_new_to_s
-    a = Exception.new("foo")
-    raise a, "bar"
-  rescue Exception => e
-    assert_equal "bar", e.to_s
-  end
-
-  def test_raises_same_instance
-    a = Exception.new("foo")
-    raise a
-  rescue Exception => e
-    assert_same e, a
-  end
-
-  def test_raises_exception_class
-    assert_raises(StandardError) { raise StandardError }
-  end
-
-  def test_raises_type_error_for_bad_args
-    assert_raises(TypeError) { raise 1 }
-  end
-
-  def test_raise_is_private
-    assert_raises(NoMethodError) do
-      Object.new.extend(RaisePlus).raise(RuntimeError)
-    end
-  end
-end