diff --git a/railties/lib/rails/generators/actions.rb b/railties/lib/rails/generators/actions.rb
index 406a5b8fc7..c3a43d5398 100644
--- a/railties/lib/rails/generators/actions.rb
+++ b/railties/lib/rails/generators/actions.rb
@@ -40,8 +40,7 @@ module Rails
         in_root do
           str = "gem #{parts.join(", ")}"
           str = indentation + str
-          str = "\n" + str
-          append_file "Gemfile", str, verbose: false
+          append_file_with_newline "Gemfile", str, verbose: false
         end
       end
 
@@ -58,9 +57,9 @@ module Rails
         log :gemfile, "group #{str}"
 
         in_root do
-          append_file "Gemfile", "\ngroup #{str} do", force: true
+          append_file_with_newline "Gemfile", "group #{str} do", force: true
           with_indentation(&block)
-          append_file "Gemfile", "\nend\n", force: true
+          append_file_with_newline "Gemfile", "end", force: true
         end
       end
 
@@ -71,9 +70,9 @@ module Rails
         log :github, "github #{str}"
 
         in_root do
-          append_file "Gemfile", "\n#{indentation}github #{str} do", force: true
+          append_file_with_newline "Gemfile", "#{indentation}github #{str} do", force: true
           with_indentation(&block)
-          append_file "Gemfile", "\n#{indentation}end", force: true
+          append_file_with_newline "Gemfile", "#{indentation}end", force: true
         end
       end
 
@@ -91,9 +90,9 @@ module Rails
 
         in_root do
           if block
-            append_file "Gemfile", "\nsource #{quote(source)} do", force: true
+            append_file_with_newline "Gemfile", "source #{quote(source)} do", force: true
             with_indentation(&block)
-            append_file "Gemfile", "\nend\n", force: true
+            append_file_with_newline "Gemfile", "end", force: true
           else
             prepend_file "Gemfile", "source #{quote(source)}\n", verbose: false
           end
@@ -344,6 +343,13 @@ module Rails
         ensure
           @indentation -= 1
         end
+
+        # Append string to a file with a newline if necessary
+        def append_file_with_newline(path, str, options = {})
+          gsub_file path, /\n?\z/, options do |match|
+            match.end_with?("\n") ? "" : "\n#{str}\n"
+          end
+        end
     end
   end
 end
diff --git a/railties/test/generators/actions_test.rb b/railties/test/generators/actions_test.rb
index 150836d4ce..607d35e023 100644
--- a/railties/test/generators/actions_test.rb
+++ b/railties/test/generators/actions_test.rb
@@ -43,7 +43,7 @@ class ActionsTest < Rails::Generators::TestCase
   def test_add_source_adds_source_to_gemfile
     run_generator
     action :add_source, "http://gems.github.com"
-    assert_file "Gemfile", /source 'http:\/\/gems\.github\.com'/
+    assert_file "Gemfile", /source 'http:\/\/gems\.github\.com'\n/
   end
 
   def test_add_source_with_block_adds_source_to_gemfile_with_gem
@@ -51,7 +51,7 @@ class ActionsTest < Rails::Generators::TestCase
     action :add_source, "http://gems.github.com" do
       gem "rspec-rails"
     end
-    assert_file "Gemfile", /source 'http:\/\/gems\.github\.com' do\n  gem 'rspec-rails'\nend/
+    assert_file "Gemfile", /source 'http:\/\/gems\.github\.com' do\n  gem 'rspec-rails'\nend\n\z/
   end
 
   def test_add_source_with_block_adds_source_to_gemfile_after_gem
@@ -60,13 +60,13 @@ class ActionsTest < Rails::Generators::TestCase
     action :add_source, "http://gems.github.com" do
       gem "rspec-rails"
     end
-    assert_file "Gemfile", /gem 'will-paginate'\nsource 'http:\/\/gems\.github\.com' do\n  gem 'rspec-rails'\nend/
+    assert_file "Gemfile", /gem 'will-paginate'\nsource 'http:\/\/gems\.github\.com' do\n  gem 'rspec-rails'\nend\n\z/
   end
 
   def test_gem_should_put_gem_dependency_in_gemfile
     run_generator
     action :gem, "will-paginate"
-    assert_file "Gemfile", /gem 'will\-paginate'/
+    assert_file "Gemfile", /gem 'will\-paginate'\n\z/
   end
 
   def test_gem_with_version_should_include_version_in_gemfile
@@ -141,7 +141,7 @@ class ActionsTest < Rails::Generators::TestCase
       gem "fakeweb"
     end
 
-    assert_file "Gemfile", /\ngroup :development, :test do\n  gem 'rspec-rails'\nend\n\ngroup :test do\n  gem 'fakeweb'\nend/
+    assert_file "Gemfile", /^group :development, :test do\n  gem 'rspec-rails'\nend\ngroup :test do\n  gem 'fakeweb'\nend\n\z/
   end
 
   def test_github_should_create_an_indented_block
@@ -153,7 +153,7 @@ class ActionsTest < Rails::Generators::TestCase
       gem "baz"
     end
 
-    assert_file "Gemfile", /\ngithub 'user\/repo' do\n  gem 'foo'\n  gem 'bar'\n  gem 'baz'\nend/
+    assert_file "Gemfile", /^github 'user\/repo' do\n  gem 'foo'\n  gem 'bar'\n  gem 'baz'\nend\n\z/
   end
 
   def test_github_should_create_an_indented_block_with_options
@@ -165,7 +165,7 @@ class ActionsTest < Rails::Generators::TestCase
       gem "baz"
     end
 
-    assert_file "Gemfile", /\ngithub 'user\/repo', a: 'correct', other: true do\n  gem 'foo'\n  gem 'bar'\n  gem 'baz'\nend/
+    assert_file "Gemfile", /^github 'user\/repo', a: 'correct', other: true do\n  gem 'foo'\n  gem 'bar'\n  gem 'baz'\nend\n\z/
   end
 
   def test_github_should_create_an_indented_block_within_a_group
@@ -179,7 +179,48 @@ class ActionsTest < Rails::Generators::TestCase
       end
     end
 
-    assert_file "Gemfile", /\ngroup :magic do\n  github 'user\/repo', a: 'correct', other: true do\n    gem 'foo'\n    gem 'bar'\n    gem 'baz'\n  end\nend\n/
+    assert_file "Gemfile", /^group :magic do\n  github 'user\/repo', a: 'correct', other: true do\n    gem 'foo'\n    gem 'bar'\n    gem 'baz'\n  end\nend\n\z/
+  end
+
+  def test_gem_with_gemfile_without_newline_at_the_end
+    run_generator
+    File.open("Gemfile", "a") { |f| f.write("gem 'rspec-rails'") }
+
+    action :gem, "will-paginate"
+    assert_file "Gemfile", /gem 'rspec-rails'\ngem 'will-paginate'\n\z/
+  end
+
+  def test_gem_group_with_gemfile_without_newline_at_the_end
+    run_generator
+    File.open("Gemfile", "a") { |f| f.write("gem 'rspec-rails'") }
+
+    action :gem_group, :test do
+      gem "fakeweb"
+    end
+
+    assert_file "Gemfile", /gem 'rspec-rails'\ngroup :test do\n  gem 'fakeweb'\nend\n\z/
+  end
+
+  def test_add_source_with_gemfile_without_newline_at_the_end
+    run_generator
+    File.open("Gemfile", "a") { |f| f.write("gem 'rspec-rails'") }
+
+    action :add_source, "http://gems.github.com" do
+      gem "fakeweb"
+    end
+
+    assert_file "Gemfile", /gem 'rspec-rails'\nsource 'http:\/\/gems\.github\.com' do\n  gem 'fakeweb'\nend\n\z/
+  end
+
+  def test_github_with_gemfile_without_newline_at_the_end
+    run_generator
+    File.open("Gemfile", "a") { |f| f.write("gem 'rspec-rails'") }
+
+    action :github, "user/repo" do
+      gem "fakeweb"
+    end
+
+    assert_file "Gemfile", /gem 'rspec-rails'\ngithub 'user\/repo' do\n  gem 'fakeweb'\nend\n\z/
   end
 
   def test_environment_should_include_data_in_environment_initializer_block