diff --git a/ChangeLog b/ChangeLog
index d6fbe0fee4..6a67299a17 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Fri Dec 21 13:09:11 2007  Tanaka Akira  <akr@fsij.org>
+
+	* encoding.c (rb_locale_charmap): return nil if no locale information.
+
 Fri Dec 21 12:55:39 2007  Tanaka Akira  <akr@fsij.org>
 
 	* lib/runit, lib/rubyunit.rb, test/testunit/runit: removed.
diff --git a/encoding.c b/encoding.c
index 07c9b42e9d..1af3c4422c 100644
--- a/encoding.c
+++ b/encoding.c
@@ -714,7 +714,7 @@ rb_locale_charmap(VALUE klass)
     codeset = nl_langinfo(CODESET);
     return rb_str_new2(codeset);
 #else
-    return rb_str_new2("ASCII-8BIT");
+    return Qnil;
 #endif
 }
 
diff --git a/ruby.c b/ruby.c
index f16ed424c8..525a3cdb19 100644
--- a/ruby.c
+++ b/ruby.c
@@ -139,9 +139,12 @@ static rb_encoding *
 locale_encoding(void)
 {
     VALUE codeset = rb_locale_charmap(Qnil);
-    char *name = StringValueCStr(codeset);
+    char *name;
     int idx;
 
+    if (codeset == Qnil)
+        return rb_default_encoding();
+
     idx = rb_enc_find_index(name);
     if (idx < 0)
         return rb_default_encoding();