diff --git a/lib/redmine/plugin.rb b/lib/redmine/plugin.rb
index 503c3db..0c0affa 100644
--- a/lib/redmine/plugin.rb
+++ b/lib/redmine/plugin.rb
@@ -19,6 +19,7 @@ module Redmine #:nodoc:
 
   class PluginNotFound < StandardError; end
   class PluginRequirementError < StandardError; end
+  class PluginDeferLoadError < StandardError; end
 
   # Base class for Redmine plugins.
   # Plugins are registered using the <tt>register</tt> class method that acts as the public constructor.
@@ -142,18 +143,50 @@ module Redmine #:nodoc:
       registered_plugins[id.to_sym].present?
     end
 
+    def self.requires_plugin(plugin_name)
+      raise PluginDeferLoadError unless installed? plugin_name
+    end
+
+    def self.load_directory(directory)
+      begin
+        restore_a = $:.dup
+        restore_b = ActiveSupport::Dependencies.autoload_paths.dup
+
+        lib = File.join(directory, "lib")
+        if File.directory?(lib)
+          $:.unshift lib
+          ActiveSupport::Dependencies.autoload_paths += [lib]
+        end
+
+        initializer = File.join(directory, "init.rb")
+        if File.file?(initializer)
+          Kernel.load initializer
+        end
+
+        true
+
+      rescue PluginDeferLoadError => e
+        $:[0..-1] = restore_a
+        ActiveSupport::Dependencies.autoload_paths = restore_b
+
+        false
+      end
+    end
+
     def self.load
+      load_queue = []
+
       Dir.glob(File.join(self.directory, '*')).sort.each do |directory|
-        if File.directory?(directory)
-          lib = File.join(directory, "lib")
-          if File.directory?(lib)
-            $:.unshift lib
-            ActiveSupport::Dependencies.autoload_paths += [lib]
-          end
-          initializer = File.join(directory, "init.rb")
-          if File.file?(initializer)
-            require initializer
-          end
+        load_queue << directory if File.directory?(directory)
+      end
+
+      while load_queue.count > 0
+        amount_before = load_queue.count
+
+        load_queue.delete_if {|directory| self.load_directory directory }
+
+        if load_queue.count == amount_before
+          raise "Could not load plugins directories #{load_queue.map{|d| File.basename d}.inspect}. Possible dependency cycle?"
         end
       end
     end