2 files changed, 9 insertions, 0 deletions
diff --git a/ChangeLog b/ChangeLog
index 58d0bbb0d0..57b881c38c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Feb  9 11:31:09 2009  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* io.c (io_encoding_set): ignore second argument when external and
+	  internal are same. [ruby-dev:37939]
+
 Sun Feb  8 23:28:05 2009  Yusuke Endoh  <mame@tsg.ne.jp>
 
 	* include/ruby/st.h, st.c: order entries by a linked list instead of
diff --git a/io.c b/io.c
index 5a91e04c6a..80482bf5fa 100644
--- a/io.c
+++ b/io.c
@@ -6969,6 +6969,10 @@ io_encoding_set(rb_io_t *fptr, VALUE v1, VALUE v2, VALUE opt)
 	    }
 	    else
 		enc = rb_to_encoding(v2);
+	    if (enc == enc2) {
+		/* Special case - "-" => no transcoding */
+		enc2 = NULL;
+	    }
 	}
 	else
 	    enc = rb_to_encoding(v2);