diff --git a/ChangeLog b/ChangeLog
index ae7b37df4c..cb186490c1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Aug 17 08:11:53 2009  Tadayoshi Funaba  <tadf@dotrb.org>
+
+	* lib/cmath.rb: use num#i.
+
 Mon Aug 17 07:59:00 2009  Tadayoshi Funaba  <tadf@dotrb.org>
 
 	* numeric.c (flo_pow,fix_pow): may return complex number.
diff --git a/lib/cmath.rb b/lib/cmath.rb
index c4b14e3ef6..b23dac239c 100644
--- a/lib/cmath.rb
+++ b/lib/cmath.rb
@@ -148,7 +148,7 @@ module CMath
     if z.real? and z >= -1 and z <= 1
       asin!(z)
     else
-      Complex(0, -1.0) * log(Complex(0, 1.0) * z + sqrt(1.0 - z * z))
+      (-1.0).i * log(1.0.i * z + sqrt(1.0 - z * z))
     end
   end
 
@@ -156,7 +156,7 @@ module CMath
     if z.real? and z >= -1 and z <= 1
       acos!(z)
     else
-      Complex(0, -1.0) * log(z + Complex(0, 1.0) * sqrt(1.0 - z * z))
+      (-1.0).i * log(z + 1.0.i * sqrt(1.0 - z * z))
     end
   end
 
@@ -164,7 +164,7 @@ module CMath
     if z.real?
       atan!(z)
     else
-      Complex(0, 1.0) * log((Complex(0, 1.0) + z) / (Complex(0, 1.0) - z)) / 2.0
+      1.0.i * log((1.0.i + z) / (1.0.i - z)) / 2.0
     end
   end
 
@@ -172,7 +172,7 @@ module CMath
     if y.real? and x.real?
       atan2!(y,x)
     else
-      Complex(0, -1.0) * log((x + Complex(0, 1.0) * y) / sqrt(x * x + y * y))
+      (-1.0).i * log((x + 1.0.i * y) / sqrt(x * x + y * y))
     end
   end