diff --git a/ChangeLog b/ChangeLog
index 23f0f89a8d..6bdeaafb9b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,12 @@
-Sat Jul  3 09:47:26 2010  Aaron Patterson <aaron@tenderlovemaking.com>
+Sat Jul  3 16:14:10 2010  Kenta Murata  <mrkn@mrkn.jp>
+
+	* ext/bigdecimal/bigdecimal.c (Init_bigdecimal): add two new constants
+	  BigDecimal::INFINITY and BigDecimal::NAN.
+
+	* ext/bigdecimal/lib/bigdecimal/math.rb (BigMath.exp): modify the
+	  behaviors for infinity arguments as same as Math.exp.
+
+Sat Jul  3 09:47:26 2010  Aaron Patterson  <aaron@tenderlovemaking.com>
 
 	* ext/psych/lib/psych/visitors/to_ruby.rb(visit_Psych_Nodes_Scalar):
 	  teaching Psych to deserialize DateTime objects. [Bug #1390]
@@ -11,7 +19,7 @@ Sat Jul  3 09:47:26 2010  Aaron Patterson <aaron@tenderlovemaking.com>
 	
 	* test/psych/test_date_time.rb: tests for dumping DateTime objects.
 
-Sat Jul  3 09:13:55 2010  Aaron Patterson <aaron@tenderlovemaking.com>
+Sat Jul  3 09:13:55 2010  Aaron Patterson  <aaron@tenderlovemaking.com>
 
 	* ext/psych/lib/psych/visitors/yaml_tree.rb (visit_Time): use
 	  Time#nsec to accurately serialize time objects. [ruby-core:29233]
diff --git a/ext/bigdecimal/bigdecimal.c b/ext/bigdecimal/bigdecimal.c
index 817fc13cfd..340ea8bb80 100644
--- a/ext/bigdecimal/bigdecimal.c
+++ b/ext/bigdecimal/bigdecimal.c
@@ -1902,6 +1902,8 @@ BigDecimal_sign(VALUE self)
 void
 Init_bigdecimal(void)
 {
+    VALUE arg;
+
     /* Initialize VP routines */
     VpInit((U_LONG)0);
 
@@ -2023,6 +2025,12 @@ Init_bigdecimal(void)
     /* -3: Indicates that a value is negative and infinite. See BigDecimal.sign. */
     rb_define_const(rb_cBigDecimal, "SIGN_NEGATIVE_INFINITE",INT2FIX(VP_SIGN_NEGATIVE_INFINITE));
 
+    arg = rb_str_new2("+Infinity");
+    rb_define_const(rb_cBigDecimal, "INFINITY", BigDecimal_global_new(1, &arg, rb_cBigDecimal));
+    arg = rb_str_new2("NaN");
+    rb_define_const(rb_cBigDecimal, "NAN", BigDecimal_global_new(1, &arg, rb_cBigDecimal));
+
+
     /* instance methods */
     rb_define_method(rb_cBigDecimal, "precs", BigDecimal_prec, 0);
 
diff --git a/ext/bigdecimal/lib/bigdecimal/math.rb b/ext/bigdecimal/lib/bigdecimal/math.rb
index 41fc69f66c..c17841fdb9 100644
--- a/ext/bigdecimal/lib/bigdecimal/math.rb
+++ b/ext/bigdecimal/lib/bigdecimal/math.rb
@@ -155,7 +155,15 @@ module BigMath
   # -> "0.271828182845904523536028752390026306410273E1"
   def exp(x, prec)
     raise ArgumentError, "Zero or negative precision for exp" if prec <= 0
-    return BigDecimal("NaN") if x.infinite? || x.nan?
+    if x.infinite?
+      if x < 0
+        return BigDecimal("0", prec)
+      else
+        return BigDecimal("+Infinity", prec)
+      end
+    elsif x.nan?
+      return BigDecimal("NaN", prec)
+    end
     n    = prec + BigDecimal.double_fig
     one  = BigDecimal("1")
     x = -x if neg = x < 0
diff --git a/test/bigdecimal/test_bigdecimal.rb b/test/bigdecimal/test_bigdecimal.rb
index b622358758..a699d0c488 100644
--- a/test/bigdecimal/test_bigdecimal.rb
+++ b/test/bigdecimal/test_bigdecimal.rb
@@ -709,4 +709,12 @@ class TestBigDecimal < Test::Unit::TestCase
   ensure
     GC.stress = stress
   end
+
+  def test_INFINITY
+    assert(BigDecimal::INFINITY.infinite?, "BigDecimal::INFINITY is not a infinity")
+  end
+
+  def test_NAN
+    assert(BigDecimal::NAN.nan?, "BigDecimal::NAN is not NaN")
+  end
 end
diff --git a/test/bigdecimal/test_bigmath.rb b/test/bigdecimal/test_bigmath.rb
index 453c47ec6b..ae3cb9d5f9 100644
--- a/test/bigdecimal/test_bigmath.rb
+++ b/test/bigdecimal/test_bigmath.rb
@@ -67,6 +67,14 @@ class TestBigMath < Test::Unit::TestCase
     assert_in_epsilon(Math.exp(40), exp(BigDecimal("40"), N))
     assert_in_epsilon(Math.exp(-N), exp(BigDecimal("-20"), N))
     assert_in_epsilon(Math.exp(-40), exp(BigDecimal("-40"), N))
+    begin
+      old_mode = BigDecimal.mode(BigDecimal::EXCEPTION_INFINITY)
+      BigDecimal.mode(BigDecimal::EXCEPTION_INFINITY, false)
+      assert(exp(BigDecimal::INFINITY, N).infinite?, "exp(INFINITY) is not an infinity")
+    ensure
+      #BigDecimal.mode(BigDecimal::EXCEPTION_INFINITY, old_mode)
+    end
+    assert_equal(0.0, exp(-BigDecimal::INFINITY, N))
   end
 
   def test_log