diff --git a/lib/thor/actions/inject_into_file.rb b/lib/thor/actions/inject_into_file.rb
index 66dd1f5fc..e0a561e13 100644
--- a/lib/thor/actions/inject_into_file.rb
+++ b/lib/thor/actions/inject_into_file.rb
@@ -16,11 +16,11 @@ module Actions
     # 
     # ==== Examples
     #
-    #   inject_into_file "config/environment.rb", "config.gem thor", :after => "Rails::Initializer.run do |config|\n"
+    #   inject_into_file "config/environment.rb", "config.gem :thor", :after => "Rails::Initializer.run do |config|\n"
     #
     #   inject_into_file "config/environment.rb", :after => "Rails::Initializer.run do |config|\n" do
     #     gems = ask "Which gems would you like to add?"
-    #     gems.split(" ").map{ |gem| "  config.gem #{gem}" }.join("\n")
+    #     gems.split(" ").map{ |gem| "  config.gem :#{gem}" }.join("\n")
     #   end
     #
     def inject_into_file(destination, *args, &block)
@@ -35,30 +35,39 @@ def inject_into_file(destination, *args, &block)
     end
 
     class InjectIntoFile < EmptyDirectory #:nodoc:
-      attr_reader :flag, :replacement
+      attr_reader :replacement
 
       def initialize(base, destination, data, config)
         super(base, destination, { :verbose => true }.merge(config))
+        @replacement = data.is_a?(Proc) ? data.call : data
+      end
 
-        data = data.call if data.is_a?(Proc)
+      def invoke!
+        say_status :inject, config[:verbose]
 
-        @replacement = if @config.key?(:after)
-          @flag = @config.delete(:after)
-          @flag + data
+        flag = if @config.key?(:after)
+          content = '\0' + replacement
+          @config[:after]
         else
-          @flag = @config.delete(:before)
-          data + @flag
+          content = replacement + '\0'
+          @config[:before]
         end
-      end
 
-      def invoke!
-        say_status :inject, config[:verbose]
-        replace!(flag, replacement)
+        replace!(flag, content)
       end
 
       def revoke!
         say_status :deinject, config[:verbose]
-        replace!(replacement, flag)
+
+        flag = if @config.key?(:after)
+          content = '\1\2'
+          /(#{Regexp.escape(@config[:after])})(.*)(#{Regexp.escape(replacement)})/m
+        else
+          content = '\2\3'
+          /(#{Regexp.escape(replacement)})(.*)(#{Regexp.escape(@config[:before])})/m
+        end
+
+        replace!(flag, content)
       end
 
       protected
diff --git a/spec/actions/inject_into_file_spec.rb b/spec/actions/inject_into_file_spec.rb
index 2fd900d59..07853d7a7 100644
--- a/spec/actions/inject_into_file_spec.rb
+++ b/spec/actions/inject_into_file_spec.rb
@@ -66,12 +66,28 @@ def file
     end
 
     it "deinjects the destination file before injection" do
-      invoke! "doc/README", "\nmore content", :before => "__start__"
-      revoke! "doc/README", "\nmore content", :before => "__start__"
+      invoke! "doc/README", "more content\n", :before => "__start__"
+      revoke! "doc/README", "more content\n", :before => "__start__"
 
       File.read(file).must == "__start__\nREADME\n__end__\n"
     end
 
+    it "deinjects even with double after injection" do
+      invoke! "doc/README", "\nmore content", :after => "__start__"
+      invoke! "doc/README", "\nanother stuff", :after => "__start__"
+      revoke! "doc/README", "\nmore content", :after => "__start__"
+
+      File.read(file).must == "__start__\nanother stuff\nREADME\n__end__\n"
+    end
+
+    it "deinjects even with double before injection" do
+      invoke! "doc/README", "more content\n", :before => "__start__"
+      invoke! "doc/README", "another stuff\n", :before => "__start__"
+      revoke! "doc/README", "more content\n", :before => "__start__"
+
+      File.read(file).must == "another stuff\n__start__\nREADME\n__end__\n"
+    end
+
     it "shows progress information to the user" do
       invoke!("doc/README", "\nmore content", :after => "__start__")
       revoke!("doc/README", "\nmore content", :after => "__start__").must == "    deinject  doc/README\n"