diff --git a/ChangeLog b/ChangeLog
index 3c436b4cab..7876775488 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+Mon Jun 13 14:35:00 2011  Kenta Murata  <mrkn@mrkn.jp>
+
+	* lib/cmath.rb (CMath.cbrt): returns the principal value of the cube
+	  root of the argument.  fix #3676
+
+	* test/test_cmath.rb (test_cbrt_returns_principal_value_of_cube_root):
+	  test for the above change.
+
 Mon Jun 13 14:17:00 2011  Kenta Murata  <mrkn@mrkn.jp>
 
 	* lib/test/unit.rb (Test::Unit::GlobOption#non_options): fix typo.
diff --git a/lib/cmath.rb b/lib/cmath.rb
index 24a0e70f9c..4751f6c4a1 100644
--- a/lib/cmath.rb
+++ b/lib/cmath.rb
@@ -122,13 +122,9 @@ module CMath
   end
 
   ##
-  # returns the cube root of +z+
+  # returns the principal value of the cube root of +z+
   def cbrt(z)
-    if z.real?
-      cbrt!(z)
-    else
-      Complex(z) ** (1.0/3)
-    end
+    Complex(z) ** (1.0/3)
   end
 
   ##
diff --git a/test/test_cmath.rb b/test/test_cmath.rb
index 46a357fab2..4f85ec3d04 100644
--- a/test/test_cmath.rb
+++ b/test/test_cmath.rb
@@ -5,4 +5,8 @@ class TestCMath < Test::Unit::TestCase
   def test_sqrt
     assert_equal CMath.sqrt(1.0.i), CMath.sqrt(1.i), '[ruby-core:31672]'
   end
+
+  def test_cbrt_returns_principal_value_of_cube_root
+    assert_equal CMath.cbrt(-8), (-8)**(1.0/3), '#3676'
+  end
 end