diff --git a/activerecord/lib/active_record/calculations.rb b/activerecord/lib/active_record/calculations.rb
index 634236e..5e33cf1 100644
--- a/activerecord/lib/active_record/calculations.rb
+++ b/activerecord/lib/active_record/calculations.rb
@@ -285,11 +285,15 @@ module ActiveRecord
           operation = operation.to_s.downcase
           case operation
             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
+            when 'sum'   then type_cast_using_column(value || '0', column)
+            when 'avg'   then value && value.to_d
+            else type_cast_using_column(value, column)
           end
         end
+
+        def type_cast_using_column(value, column)
+          column ? column.type_cast(value) : value
+        end
     end
   end
 end
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index 754fd58..0fa6150 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -18,8 +18,8 @@ class CalculationsTest < ActiveRecord::TestCase

   def test_should_average_field
     value = Account.average(:credit_limit)
-    assert_kind_of Float, value
-    assert_in_delta 53.0, value, 0.001
+    assert_kind_of BigDecimal, value
+    assert_equal BigDecimal.new('53.0'), value
   end

   def test_should_return_nil_as_average
@@ -273,7 +273,7 @@ class CalculationsTest < ActiveRecord::TestCase
   end

   def test_should_sum_expression
-    assert_equal 636, Account.sum("2 * credit_limit")
+    assert_equal '636', Account.sum("2 * credit_limit")
   end

   def test_count_with_from_option