diff --git a/ChangeLog b/ChangeLog
index b7abd59970..fb0ef627cf 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -9,6 +9,13 @@ Sun Feb 17 21:39:24 2002  Tetsuya Watanabe  <tetsuya.watanabe@nifty.com>
 
 	* ext/digest/sha2/sha2init.c (Init_sha2): ditto.
 
+Sun Feb 17 18:10:09 2002  Nobuyoshi Nakada  <nobu.nakada@nifty.ne.jp>
+
+	* class.c (rb_define_class): warn unless superclass is specified
+	  explicitly.
+
+	* class.c (rb_define_class_under): ditto.
+
 Fri Feb 15 14:40:38 2002  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* eval.c (rb_eval): replace rb_cvar_declare() by rb_cvar_set().
diff --git a/class.c b/class.c
index b35e1f82e6..32ee98be72 100644
--- a/class.c
+++ b/class.c
@@ -193,6 +193,9 @@ rb_define_class(name, super)
 	}
 	return klass;
     }
+    if (!super) {
+	rb_warn("no super class for `%s', Object assumed", name);
+    }
     klass = rb_define_class_id(id, super);
     rb_class_inherited(super, klass);
     st_add_direct(rb_class_tbl, id, klass);
@@ -220,6 +223,10 @@ rb_define_class_under(outer, name, super)
 	}
 	return klass;
     }
+    if (!super) {
+	rb_warn("no super class for `%s::%s', Object assumed",
+		rb_class2name(outer), name);
+    }
     klass = rb_define_class_id(id, super);
     rb_set_class_path(klass, outer, name);
     rb_class_inherited(super, klass);