diff --git a/ChangeLog b/ChangeLog
index a26c00fd1a..5b006d591f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Mon Jul 13 22:49:50 2009  Yuki Sonoda (Yugui)  <yugui@yugui.jp>
+
+	* lib/prime.rb (Prime#prime_division): now decomposes
+	  negative integer into a decomposition with element [-1, 1].
+
+	* test/test_prime.rb: test for it.
+
 Mon Jul 13 22:28:03 2009  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* io.c (pipe_open): handles leaked on win32 when an error occurs.
diff --git a/lib/prime.rb b/lib/prime.rb
index 4114beb292..c8c9265571 100644
--- a/lib/prime.rb
+++ b/lib/prime.rb
@@ -194,7 +194,12 @@ class Prime
   #
   def prime_division(value, generator= Prime::Generator23.new)
     raise ZeroDivisionError if value == 0
-    pv = []
+    if value < 0
+      value = -value
+      pv = [[-1, 1]]
+    else
+      pv = []
+    end
     for prime in generator
       count = 0
       while (value1, mod = value.divmod(prime)
diff --git a/test/test_prime.rb b/test/test_prime.rb
index 0dad7cf987..d7c3bf5720 100644
--- a/test/test_prime.rb
+++ b/test/test_prime.rb
@@ -98,10 +98,15 @@ class TestPrime < Test::Unit::TestCase
     def test_prime_division
       pd = PRIMES.inject(&:*).prime_division
       assert_equal PRIMES.map{|p| [p, 1]}, pd
+
+      pd = (-PRIMES.inject(&:*)).prime_division
+      assert_equal [-1, *PRIMES].map{|p| [p, 1]}, pd
     end
 
     def test_from_prime_division
       assert_equal PRIMES.inject(&:*), Integer.from_prime_division(PRIMES.map{|p| [p,1]})
+
+      assert_equal -PRIMES.inject(&:*), Integer.from_prime_division([[-1, 1]] + PRIMES.map{|p| [p,1]})
     end
 
     def test_prime?
diff --git a/version.h b/version.h
index a3355dc0fb..faeea31093 100644
--- a/version.h
+++ b/version.h
@@ -4,7 +4,7 @@
 #define RUBY_VERSION_MAJOR 1
 #define RUBY_VERSION_MINOR 9
 #define RUBY_VERSION_TEENY 1
-#define RUBY_PATCHLEVEL 234
+#define RUBY_PATCHLEVEL 235
 #define RUBY_RELEASE_YEAR 2009
 #define RUBY_RELEASE_MONTH 7
 #define RUBY_RELEASE_DAY 12