diff --git a/src/core/Base.js b/src/core/Base.js
index b6f580a1..009c779f 100644
--- a/src/core/Base.js
+++ b/src/core/Base.js
@@ -40,9 +40,13 @@ this.Base = Base.inject(/** @lends Base# */{
 	 */
 	toString: function() {
 		return '{ ' + Base.each(this, function(value, key) {
-			var type = typeof value;
-			this.push(key + ': ' + (type === 'number' ? Base.formatNumber(value)
-					: type === 'string' ? "'" + value + "'" : value));
+			// Hide internal properties even if they are enumerable
+			if (key.charAt(0) != '_') {
+				var type = typeof value;
+				this.push(key + ': ' + (type === 'number'
+						? Base.formatNumber(value)
+						: type === 'string' ? "'" + value + "'" : value));
+			}
 		}, []).join(', ') + ' }';
 	},