diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index 1fe697a227e67..e24736646f12d 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Fixed Time#at_beginning_of_week returned the next Monday instead of the previous one when called on a Sunday #1403 [jean.helou@gmail.com]
+
 * Increased the speed of indifferent hash access by using Hash#default.  #1436 [Nicholas Seckar]
 
 * Added that "   " is now also blank? (using strip if available)
diff --git a/activesupport/lib/active_support/core_ext/time/calculations.rb b/activesupport/lib/active_support/core_ext/time/calculations.rb
index 1c9a3523a97c0..8247003ca3862 100644
--- a/activesupport/lib/active_support/core_ext/time/calculations.rb
+++ b/activesupport/lib/active_support/core_ext/time/calculations.rb
@@ -87,7 +87,8 @@ def next_month
         
         # Returns a new Time representing the "start" of this week (Monday, 0:00)
         def beginning_of_week
-          (self - self.wday.days).midnight + 1.day
+          days_to_monday = self.wday!=0 ? self.wday-1 : 6
+          (self - days_to_monday.days).midnight
         end
         alias :monday :beginning_of_week
         alias :at_beginning_of_week :beginning_of_week
diff --git a/activesupport/test/core_ext/time_ext_test.rb b/activesupport/test/core_ext/time_ext_test.rb
index 18ae3219bc397..6be1a70f942d0 100644
--- a/activesupport/test/core_ext/time_ext_test.rb
+++ b/activesupport/test/core_ext/time_ext_test.rb
@@ -13,6 +13,13 @@ def test_seconds_since_midnight
 
   def test_begining_of_week
     assert_equal Time.local(2005,1,31), Time.local(2005,2,4,10,10,10).beginning_of_week
+    assert_equal Time.local(2005,11,28), Time.local(2005,11,28,0,0,0).beginning_of_week #monday
+    assert_equal Time.local(2005,11,28), Time.local(2005,11,29,0,0,0).beginning_of_week #tuesday
+    assert_equal Time.local(2005,11,28), Time.local(2005,11,30,0,0,0).beginning_of_week #wednesday
+    assert_equal Time.local(2005,11,28), Time.local(2005,12,01,0,0,0).beginning_of_week #thursday
+    assert_equal Time.local(2005,11,28), Time.local(2005,12,02,0,0,0).beginning_of_week #friday
+    assert_equal Time.local(2005,11,28), Time.local(2005,12,03,0,0,0).beginning_of_week #saturday
+    assert_equal Time.local(2005,11,28), Time.local(2005,12,04,0,0,0).beginning_of_week #sunday    
   end
   
   def test_beginning_of_day