diff --git a/activerecord/lib/active_record/calculations.rb b/activerecord/lib/active_record/calculations.rb
index 889b7845fb..caa8c539d5 100644
--- a/activerecord/lib/active_record/calculations.rb
+++ b/activerecord/lib/active_record/calculations.rb
@@ -265,8 +265,9 @@ module ActiveRecord
         def type_cast_calculated_value(value, column, operation = nil)
           operation = operation.to_s.downcase
           case operation
-            when 'count', 'sum' then value.to_i
-            when 'avg'          then value && value.to_f
+            when 'count' then value.to_i
+            when 'sum'   then value =~ /\./ ? value.to_f : value.to_i
+            when 'avg'   then value && value.to_f
             else column ? column.type_cast(value) : value
           end
         end
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index 5cf655f7b7..aefb13ea9a 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -102,6 +102,11 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_equal 0, companies(:rails_core).companies.sum(:id, :conditions => '1 = 2')
   end
 
+  def test_sum_should_return_valid_values_for_decimals
+    NumericData.create(:bank_balance => 19.83)
+    assert_equal 19.83, NumericData.sum(:bank_balance)
+  end
+
   def test_should_group_by_summed_field_with_conditions
     c = Account.sum(:credit_limit, :conditions => 'firm_id > 1',
                                    :group => :firm_id)