diff --git a/lib/groupdate.rb b/lib/groupdate.rb
index cfab053..bca3bad 100644
--- a/lib/groupdate.rb
+++ b/lib/groupdate.rb
@@ -21,3 +21,12 @@ module ActiveRecord
 
   end
 end
+
+module Groupdate
+  mattr_accessor :week_starts_with
+  @@week_starts_with = :sun
+
+  def self.configure
+    yield self
+  end
+end
diff --git a/lib/groupdate/scopes.rb b/lib/groupdate/scopes.rb
index b856c23..749e2e9 100644
--- a/lib/groupdate/scopes.rb
+++ b/lib/groupdate/scopes.rb
@@ -19,7 +19,7 @@ module Groupdate
         end
 
         # for week
-        week_start = [:mon, :tue, :wed, :thu, :fri, :sat, :sun].index((options[:start] || :sun).to_sym)
+        week_start = [:mon, :tue, :wed, :thu, :fri, :sat, :sun].index((options[:start] || Groupdate.week_starts_with).to_sym)
         if field == "week" and !week_start
           raise "Unrecognized :start option"
         end
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 6eec017..a8fc0f6 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -32,6 +32,8 @@ end
 
 module TestGroupdate
 
+  @@default_config = Hash[Groupdate.class_variables.collect { |opt| [opt[2..-1].to_sym, Groupdate.class_variable_get(opt)] }]
+
   # second
 
   def test_second_end_of_second
@@ -134,6 +136,32 @@ module TestGroupdate
     assert_result_time :week, "2013-03-16 00:00:00 PDT", "2013-03-16 07:00:00", true, :start => :sat
   end
 
+  # config week starting key
+
+  def test_week_start_of_week_mon_from_config
+    with_config :week_starts_with => :mon do
+      assert_result_time :week, "2013-03-25 00:00:00 UTC", "2013-03-25 00:00:00", false
+    end
+  end
+
+  def test_week_end_of_week_mon_from_config
+    with_config :week_starts_with => :mon do
+      assert_result_time :week, "2013-03-18 00:00:00 UTC", "2013-03-24 23:59:59", false
+    end
+  end
+
+  def test_week_end_of_week_with_time_zone_mon_from_config
+    with_config :week_starts_with => :mon do
+      assert_result_time :week, "2013-03-11 00:00:00 PDT", "2013-03-18 06:59:59", true
+    end
+  end
+
+  def test_week_start_of_week_with_time_zone_mon_from_config
+    with_config :week_starts_with => :mon do
+      assert_result_time :week, "2013-03-18 00:00:00 PDT", "2013-03-18 07:00:00", true
+    end
+  end
+
   # month
 
   def test_month_end_of_month
@@ -372,4 +400,19 @@ module TestGroupdate
     User.delete_all
   end
 
+  def with_config(config)
+    setup_config config
+    yield
+  ensure
+    setup_config @@default_config
+  end
+
+private
+
+  def setup_config(config)
+    config.each do |option, value|
+      Groupdate.send "#{option}=", value
+    end
+  end
+
 end
--
libgit2 0.21.0