diff --git a/activerecord/Rakefile b/activerecord/Rakefile
index 7feb0b75a03c4..a29d7b0e99da6 100644
--- a/activerecord/Rakefile
+++ b/activerecord/Rakefile
@@ -114,6 +114,16 @@ namespace :postgresql do
     config = ARTest.config['connections']['postgresql']
     %x( createdb -E UTF8 #{config['arunit']['database']} )
     %x( createdb -E UTF8 #{config['arunit2']['database']} )
+
+    # prepare hstore
+    version = %x( createdb --version ).strip.gsub(/(.*)(\d\.\d\.\d)$/, "\\2")
+    %w(arunit arunit2).each do |db|
+      if version < "9.1.0"
+        puts "Please prepare hstore data type. See http://www.postgresql.org/docs/9.0/static/hstore.html"
+      else
+        %x( psql #{config[db]['database']} -c "CREATE EXTENSION hstore;" )
+      end
+    end
   end
 
   desc 'Drop the PostgreSQL test databases'
diff --git a/guides/source/contributing_to_ruby_on_rails.textile b/guides/source/contributing_to_ruby_on_rails.textile
index acf75d41cd8f0..92c607b6f596b 100644
--- a/guides/source/contributing_to_ruby_on_rails.textile
+++ b/guides/source/contributing_to_ruby_on_rails.textile
@@ -190,6 +190,8 @@ $ rake postgresql:build_databases
 
 NOTE: Using the rake task to create the test databases ensures they have the correct character set and collation.
 
+NOTE: You'll see the following warning (or localized warning) during activating HStore extension in PostgreSQL 9.1.x or earlier: "WARNING: => is deprecated as an operator".
+
 If you’re using another database, check the files under +activerecord/test/connections+ for default connection information. You can edit these files to provide different credentials on your machine if you must, but obviously you should not push any such changes back to Rails.
 
 You can now run the tests as you did for +sqlite3+. The tasks are respectively