diff --git a/app/models/plugin.rb b/app/models/plugin.rb
index 9511e00..0d257ad 100644
--- a/app/models/plugin.rb
+++ b/app/models/plugin.rb
@@ -100,11 +100,6 @@ class Plugin
     "https://rubygems.org/gems/#{gem_name}"
   end
 
-  def self.gemfile_changed?
-    # if true, rails server needs to restart. new installed/removed gems are.
-    @initial_gemfile_content != File.read(gemfile_path)
-  end
-
   def self.installed
     return [] unless File.exist?(gemfile_path)
     File.read(gemfile_path).scan(/"(.*?)", "(.*?)"/).map do |plugin|
@@ -136,16 +131,6 @@ class Plugin
     Rails.root + "Gemfile.plugins"
   end
 
-  def self.pristine!
-    unless File.exists?(gemfile_path)
-      File.open(gemfile_path, "w") do |f|
-        f.write "# USED BY fluentd-ui internally\n"
-      end
-    end
-    @initial_gemfile_content = File.read(gemfile_path)
-  end
-  pristine!
-
   def gemfile_path
     self.class.gemfile_path
   end
diff --git a/spec/models/plugin_spec.rb b/spec/models/plugin_spec.rb
index e9867b5..be874bc 100644
--- a/spec/models/plugin_spec.rb
+++ b/spec/models/plugin_spec.rb
@@ -9,7 +9,6 @@ describe Plugin do
 
   after do
     File.unlink Plugin.gemfile_path if File.exist?(Plugin.gemfile_path)
-    Plugin.pristine!
   end
 
   describe "#valid?" do
@@ -104,7 +103,6 @@ describe Plugin do
         plugin.install!
       end
 
-      it { Plugin.should be_gemfile_changed }
       it { plugin.should be_installed }
     end
   end
@@ -115,7 +113,6 @@ describe Plugin do
     before do
       installed_plugin.stub(:fluent_gem).and_return(true)
       installed_plugin.install!
-      Plugin.pristine!
     end
 
     before do
@@ -123,7 +120,6 @@ describe Plugin do
     end
 
     it { installed_plugin.should_not be_installed }
-    it { Plugin.should be_gemfile_changed }
   end
 
   describe "#upgrade!" do
@@ -134,12 +130,10 @@ describe Plugin do
     before do
       Plugin.any_instance.stub(:fluent_gem).and_return(true) # NOTE: not `plugin.stub` because upgrade! creates new Plugin instance internally
       installed_plugin.install!
-      Plugin.pristine!
       installed_plugin.upgrade!(target_version)
     end
 
     it { installed_plugin.should be_installed }
-    it { Plugin.should be_gemfile_changed }
     it { installed_plugin.installed_version.should == target_version }
   end