diff --git a/ChangeLog b/ChangeLog
index b1cfa903cc..7803c5edcf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Jul 21 12:39:15 2010  Yusuke Endoh  <mame@tsg.ne.jp>
+
+	* lib/cmath.rb (CMath#cbrt): cbrt should accept a negative real
+	  numbers.  [ruby-core:31234]
+
 Thu Jul 15 21:43:35 2010  Yusuke Endoh  <mame@tsg.ne.jp>
 
 	* numeric.c (fix_divide): must not use rb_rational_new1 for coercion
diff --git a/lib/cmath.rb b/lib/cmath.rb
index b23dac239c..976f269299 100644
--- a/lib/cmath.rb
+++ b/lib/cmath.rb
@@ -85,7 +85,7 @@ module CMath
   end
 
   def cbrt(z)
-    if z.real? and z >= 0
+    if z.real?
       cbrt!(z)
     else
       Complex(z) ** (1.0/3)