diff --git a/ChangeLog b/ChangeLog
index 54d3067c8d..e83b5a7046 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Wed Jul  8 19:10:22 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* error.c (rb_check_type): rejects typed data.
+
 Wed Jul  8 18:28:04 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* proc.c ({proc,binding,method}_data_type): typed.
diff --git a/error.c b/error.c
index c3738db856..c4f4938cc6 100644
--- a/error.c
+++ b/error.c
@@ -282,12 +282,14 @@ rb_check_type(VALUE x, int t)
     const struct types *type = builtin_types;
     const struct types *const typeend = builtin_types +
 	sizeof(builtin_types) / sizeof(builtin_types[0]);
+    int xt;
 
     if (x == Qundef) {
 	rb_bug("undef leaked to the Ruby space");
     }
 
-    if (TYPE(x) != t) {
+    xt = TYPE(x);
+    if (xt != t || (xt == T_DATA && RTYPEDDATA_P(x))) {
 	while (type < typeend) {
 	    if (type->type == t) {
 		const char *etype;