diff --git a/ChangeLog b/ChangeLog
index ea57286ff7..2c569b6a59 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Oct 16 12:03:31 2009  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* lib/csv.rb (CSV#raw_encoding): returns ASCII-8BIT when the io
+	  doesn't have encoding.
+
 Fri Oct 16 03:15:52 2009  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* lib/csv.rb (CSV#read_to_char): set encoding and verify data
diff --git a/lib/csv.rb b/lib/csv.rb
index 8545e661b1..d44e4db744 100644
--- a/lib/csv.rb
+++ b/lib/csv.rb
@@ -2288,8 +2288,10 @@ class CSV
       @io.internal_encoding || @io.external_encoding
     elsif @io.is_a? StringIO
       @io.string.encoding
-    else
+    elsif @io.respond_to? :encoding
       @io.encoding
+    else
+      Encoding::ASCII_8BIT
     end
   end