diff --git a/ical.js b/ical.js
index 024625b..4e303c0 100755
--- a/ical.js
+++ b/ical.js
@@ -283,7 +283,7 @@
 
         var par = stack.pop()
 
-        if (curr.uid)
+        if (curr.uid && typeof curr.uid === 'string')
         {
         	// If this is the first time we run into this UID, just save it.
         	if (par[curr.uid] === undefined)