diff --git a/ChangeLog b/ChangeLog
index dc8c2ce749..f7bb1ce0d0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Aug  1 09:44:25 2010  Tanaka Akira  <akr@fsij.org>
+
+	* class.c (rb_include_module): don't clear the method cache if the
+	  included module has no method.
+
 Sun Aug  1 09:21:32 2010  Tanaka Akira  <akr@fsij.org>
 
 	* ext/pathname/pathname.c (path_sub): Pathname#sub translated
diff --git a/class.c b/class.c
index 7e2f40b0a3..9ad8ec8539 100644
--- a/class.c
+++ b/class.c
@@ -659,7 +659,8 @@ rb_include_module(VALUE klass, VALUE module)
 	    }
 	}
 	c = RCLASS_SUPER(c) = include_class_new(module, RCLASS_SUPER(c));
-	changed = 1;
+	if (RMODULE_M_TBL(module) && RMODULE_M_TBL(module)->num_entries)
+	    changed = 1;
       skip:
 	module = RCLASS_SUPER(module);
     }