diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index b6c60d535d08a..b98369ac7dd4d 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -1,5 +1,7 @@
 *2.2.3 (next release)*
 
+* TimeWithZone#- gives correct result with wrapped DateTime, and with DateTime argument [Geoff Buesing]
+
 * Multibyte: add multibyte-safe Chars#ord rather than falling back to String#ord.  #1483 [Jason Cheow]
 
 
diff --git a/activesupport/lib/active_support/time_with_zone.rb b/activesupport/lib/active_support/time_with_zone.rb
index a02cd81f7234e..2d6390ba0aa80 100644
--- a/activesupport/lib/active_support/time_with_zone.rb
+++ b/activesupport/lib/active_support/time_with_zone.rb
@@ -198,7 +198,7 @@ def -(other)
       # If we're subtracting a Duration of variable length (i.e., years, months, days), move backwards from #time,
       # otherwise move backwards #utc, for accuracy when moving across DST boundaries
       if other.acts_like?(:time)
-        utc - other
+        utc.to_f - other.to_f
       elsif duration_of_variable_length?(other)
         method_missing(:-, other)
       else
diff --git a/activesupport/test/core_ext/time_with_zone_test.rb b/activesupport/test/core_ext/time_with_zone_test.rb
index 774fd57ee674a..806f64aa37a9c 100644
--- a/activesupport/test/core_ext/time_with_zone_test.rb
+++ b/activesupport/test/core_ext/time_with_zone_test.rb
@@ -258,6 +258,15 @@ def test_minus_with_time_with_zone
     twz2 = ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 2), ActiveSupport::TimeZone['UTC'] )
     assert_equal  86_400.0,  twz2 - twz1
   end
+  
+  def test_minus_with_datetime
+    assert_equal  86_400.0,  ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 2), ActiveSupport::TimeZone['UTC'] ) - DateTime.civil(2000, 1, 1)
+  end
+
+  def test_minus_with_wrapped_datetime
+    assert_equal  86_400.0,  ActiveSupport::TimeWithZone.new( DateTime.civil(2000, 1, 2), ActiveSupport::TimeZone['UTC'] ) - Time.utc(2000, 1, 1)
+    assert_equal  86_400.0,  ActiveSupport::TimeWithZone.new( DateTime.civil(2000, 1, 2), ActiveSupport::TimeZone['UTC'] ) - DateTime.civil(2000, 1, 1)
+  end
 
   def test_plus_and_minus_enforce_spring_dst_rules
     silence_warnings do # silence warnings raised by tzinfo gem