diff --git a/lib/parse/index.js b/lib/parse/index.js
index 053f0596..e700021e 100644
--- a/lib/parse/index.js
+++ b/lib/parse/index.js
@@ -581,12 +581,14 @@ function addParent(obj, parent) {
   var isNode = obj && typeof obj.type === 'string';
   var childParent = isNode ? obj : parent;
 
-  for (var k in obj) {
-    var value = obj[k];
-    if (Array.isArray(value)) {
-      value.forEach(function(v) { addParent(v, childParent); });
-    } else if (value && typeof value === 'object') {
-      addParent(value, childParent);
+  if (typeof obj !== 'string') {
+    for (var k in obj) {
+      var value = obj[k];
+      if (Array.isArray(value)) {
+        value.forEach(function(v) { addParent(v, childParent); });
+      } else if (value && typeof value === 'object') {
+        addParent(value, childParent);
+      }
     }
   }