diff --git a/ChangeLog b/ChangeLog
index e0ad59657f..39a22da53a 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Dec 18 17:53:05 2002  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* class.c (rb_include_module): argument should be T_MODULE, not
+	  T_class, nor T_ICLASS.
+
 Mon Dec 16 16:35:28 2002  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* stable version 1.6.8 release candidate.
diff --git a/class.c b/class.c
index 670c8b2075..5742ec3fdc 100644
--- a/class.c
+++ b/class.c
@@ -323,12 +323,7 @@ rb_include_module(klass, module)
     if (NIL_P(module)) return;
     if (klass == module) return;
 
-    switch (TYPE(module)) {
-      case T_MODULE:
-      case T_CLASS:
-      case T_ICLASS:
-	break;
-      default:
+    if (TYPE(module) != T_MODULE) {
 	Check_Type(module, T_MODULE);
     }