diff --git a/boot/boot.js b/boot/boot.js
index 62b85cffc..1a41b4d07 100644
--- a/boot/boot.js
+++ b/boot/boot.js
@@ -812,6 +812,7 @@ $tw.Tiddler = function(/* [fields,] fields */) {
 	}
 	// Freeze the tiddler against modification
 	Object.freeze(this.fields);
+	Object.freeze(this);
 };
 
 $tw.Tiddler.prototype.hasField = function(field) {