diff --git a/ChangeLog b/ChangeLog
index 44eec7aa32..d203d7d906 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Tue Mar  8 16:45:31 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* hash.c (ruby_setenv): MSDN says that Windows XP or earlier limits
+	  the total size of environment block to 5,120 chars.  and on such
+	  OS, putenv() causes SEGV.  So, ruby should limit the size of an
+	  environment variable to 5,120 bytes for workaround.
+
 Tue Mar  8 15:57:20 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* test/rubygems/test_gem_spec_fetcher.rb
diff --git a/hash.c b/hash.c
index 909263357a..f86152ae70 100644
--- a/hash.c
+++ b/hash.c
@@ -2206,6 +2206,7 @@ ruby_setenv(const char *name, const char *value)
 	rb_sys_fail("ruby_setenv");
     }
     if (value) {
+	if (strlen(value) > 5120) goto fail;
 	buf = rb_sprintf("%s=%s", name, value);
     }
     else {