diff --git a/ChangeLog b/ChangeLog
index 7ae41f2bcf..01760472e9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Apr 25 11:02:20 2010  wanabe  <s.wanabe@gmail.com>
+
+	* hash.c (ruby_setenv): putenv on msvcrt.dll can't remove empty value.
+
 Sat Apr 24 23:40:50 2010  Tanaka Akira  <akr@fsij.org>
 
 	* lib/pp.rb: use [""].pack("p").size to detect the pointer size.
diff --git a/hash.c b/hash.c
index 0b863bd637..21344c5e57 100644
--- a/hash.c
+++ b/hash.c
@@ -2129,6 +2129,7 @@ ruby_setenv(const char *name, const char *value)
 	buf = ALLOCA_N(char, len);
 	snprintf(buf, len, "%s=", name);
 	putenv(buf);
+	SetEnvironmentVariable(name, 0);
     }
 #elif defined(HAVE_SETENV) && defined(HAVE_UNSETENV)
 #undef setenv