diff --git a/ext/bigdecimal/lib/bigdecimal/util.rb b/ext/bigdecimal/lib/bigdecimal/util.rb
index 0c4e486..58f5ac2 100644
--- a/ext/bigdecimal/lib/bigdecimal/util.rb
+++ b/ext/bigdecimal/lib/bigdecimal/util.rb
@@ -1,4 +1,26 @@
 # frozen_string_literal: false
+
+# BigDecimal extends the native NilClass class to provide the #to_d method.
+#
+# When you require BigDecimal in your application, this method will be available
+# on nil.
+class NilClass
+  # call-seq:
+  #     nil.to_d  -> 0
+  #
+  # Always return 0 in BigDecimal.
+  #
+  #     require 'bigdecimal'
+  #     require 'bigdecimal/util'
+  #
+  #     nil.to_d
+  #     # => #<BigDecimal:7ffa299205d8,'0.0',9(27)>
+  #
+  def to_d
+    BigDecimal(0)
+  end
+end
+
 # BigDecimal extends the native Integer class to provide the #to_d method.
 #
 # When you require the BigDecimal library in your application, this methodwill
diff --git a/test/bigdecimal/test_bigdecimal_util.rb b/test/bigdecimal/test_bigdecimal_util.rb
index c3a45b2..d7d60b2 100644
--- a/test/bigdecimal/test_bigdecimal_util.rb
+++ b/test/bigdecimal/test_bigdecimal_util.rb
@@ -9,6 +9,10 @@ def test_BigDecimal_to_d
     assert_same(x, x.to_d)
   end
 
+  def test_NilClass_to_d
+    assert_equal(BigDecimal(0), nil.to_d)
+  end
+
   def test_Integer_to_d
     assert_equal(BigDecimal(1), 1.to_d)
     assert_equal(BigDecimal(2<<100), (2<<100).to_d)