diff --git a/ChangeLog b/ChangeLog
index 03468dc571..17220f5ae5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu May 29 22:29:39 2008  Yusuke Endoh  <mame@tsg.ne.jp>
+
+	* io.c (argf_external_encoding, argf_internal_encoding): fix SEGV by
+	  ARGF.external_encoding.
+
 Wed May 28 18:05:28 2008  Akinori MUSHA  <knu@iDaemons.org>
 
 	* array.c (rb_ary_nitems, Init_Array): Axe Array#nitems().
diff --git a/io.c b/io.c
index 0b4b4b64b2..e4a0c21c19 100644
--- a/io.c
+++ b/io.c
@@ -6942,13 +6942,19 @@ rb_io_set_encoding(int argc, VALUE *argv, VALUE io)
 static VALUE
 argf_external_encoding(VALUE argf)
 {
-    return rb_io_external_encoding(current_file);
+    if (!RTEST(current_file)) {
+	return rb_enc_from_encoding(rb_default_external_encoding());
+    }
+    return rb_io_external_encoding(rb_io_check_io(current_file));
 }
 
 static VALUE
 argf_internal_encoding(VALUE argf)
 {
-    return rb_io_internal_encoding(current_file);
+    if (!RTEST(current_file)) {
+	return rb_enc_from_encoding(rb_default_external_encoding());
+    }
+    return rb_io_internal_encoding(rb_io_check_io(current_file));
 }
 
 static VALUE