diff --git a/ChangeLog b/ChangeLog
index 920a94fb31..a5c2a5b03b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Aug 14 11:27:37 2003  NAKAMURA Usaku <usa@ruby-lang.org>
+
+	* gc.c (rb_data_object_alloc): check type of 1st argument.
+	  [ruby-dev:21192]
+
 Wed Aug 13 23:31:00 2003  Shigeo Kobayashi  <shigek@ruby-lang.org>
 
 	* ext/bigdecimal.c .h .html: Ambiguity of BigDecimal::limit removed.
diff --git a/gc.c b/gc.c
index 1f8970eed7..a76d5c81bc 100644
--- a/gc.c
+++ b/gc.c
@@ -342,6 +342,7 @@ rb_data_object_alloc(klass, datap, dmark, dfree)
     RUBY_DATA_FUNC dfree;
 {
     NEWOBJ(data, struct RData);
+    Check_Type(klass, T_CLASS);
     OBJSETUP(data, klass, T_DATA);
     data->data = datap;
     data->dfree = dfree;