diff --git a/ChangeLog b/ChangeLog
index 23966b9f29..76e8e3325d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Jan  1 17:50:47 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* io.c (rb_io_mode_enc): encoding spec is not allowed in binary mode.
+	  [ruby-dev:32913]
+
 Tue Jan  1 14:41:56 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* lib/rexml: 1.9 patch from Sam Ruby mentioned in his blog:
diff --git a/io.c b/io.c
index a5a5f93743..18d651ea8f 100644
--- a/io.c
+++ b/io.c
@@ -3192,6 +3192,9 @@ rb_io_mode_enc(rb_io_t *fptr, const char *mode)
 {
     const char *p = strchr(mode, ':');
     if (p) {
+	if (fptr->mode & FMODE_BINMODE) {
+	    rb_raise(rb_eArgError, "encoding in binary mode");
+	}
 	mode_enc(fptr, p+1);
     }
 }