diff --git a/activesupport/lib/active_support/core_ext/big_decimal/conversions.rb b/activesupport/lib/active_support/core_ext/big_decimal/conversions.rb
index f7f03f4d95..3720dbb8b8 100644
--- a/activesupport/lib/active_support/core_ext/big_decimal/conversions.rb
+++ b/activesupport/lib/active_support/core_ext/big_decimal/conversions.rb
@@ -18,6 +18,10 @@ class BigDecimal
     end
   end
 
+  def to_d
+    self
+  end
+
   DEFAULT_STRING_FORMAT = 'F'
   def to_formatted_s(format = DEFAULT_STRING_FORMAT)
     _original_to_s(format)
diff --git a/activesupport/test/core_ext/bigdecimal.rb b/activesupport/test/core_ext/bigdecimal_test.rb
similarity index 83%
rename from activesupport/test/core_ext/bigdecimal.rb
rename to activesupport/test/core_ext/bigdecimal_test.rb
index 9faad9146f..0272f564de 100644
--- a/activesupport/test/core_ext/bigdecimal.rb
+++ b/activesupport/test/core_ext/bigdecimal_test.rb
@@ -7,4 +7,9 @@ class BigDecimalTest < Test::Unit::TestCase
     assert_equal("--- .NaN\n", BigDecimal.new('NaN').to_yaml)
     assert_equal("--- -.Inf\n", BigDecimal.new('-Infinity').to_yaml)
   end
-end
\ No newline at end of file
+
+  def test_to_d
+    bd = BigDecimal.new '10'
+    assert_equal bd, bd.to_d
+  end
+end