diff --git a/IPython/html/static/widgets/js/widget.js b/IPython/html/static/widgets/js/widget.js
index a3df7e0..ea5c062 100644
--- a/IPython/html/static/widgets/js/widget.js
+++ b/IPython/html/static/widgets/js/widget.js
@@ -236,7 +236,7 @@ define(["widgets/js/manager",
                     packed.push(that._pack_models(sub_value));
                 });
                 return packed;
-            } else if (value instanceof Date) {
+            } else if (value instanceof Date || value instanceof String) {
                 return value;
             } else if (value instanceof Object) {
                 packed = {};