diff --git a/ChangeLog b/ChangeLog
index 3e6b0a0145..d16b94f7ea 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Aug 26 23:53:23 2003  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* lib/ostruct.rb (OpenStruct::method_missing): prohibit modifying
+	  frozen OpenStruct. [ruby-talk:80214]
+
 Tue Aug 26 20:03:50 2003  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* lib/mkmf.rb (create_tmpsrc): add the hook for source.
diff --git a/lib/ostruct.rb b/lib/ostruct.rb
index 50a7ceca12..b1ae641dcb 100644
--- a/lib/ostruct.rb
+++ b/lib/ostruct.rb
@@ -25,6 +25,9 @@ class OpenStruct
       if len != 1
 	raise ArgumentError, "wrong # of arguments (#{len} for 1)", caller(1)
       end
+      if self.frozen?
+	raise TypeError, "can't modify frozen #{self.class}", caller(1)
+      end
       mname.chop!
       @table[mname.intern] = args[0]
     elsif len == 0