diff --git a/src/view.transform.js b/src/view.transform.js
index 3c8aa262..0b9a1a8a 100644
--- a/src/view.transform.js
+++ b/src/view.transform.js
@@ -44,7 +44,11 @@ my.Transform = Backbone.View.extend({
     // Put in the basic (identity) transform script
     // TODO: put this into the template?
     var editor = this.el.find('.expression-preview-code');
-    var col = this.model.fields.models[0].id;
+    if (this.model.fields.length > 0) {
+      var col = this.model.fields.models[0].id;
+    } else {
+      var col = 'unknown';
+    }
     editor.val("function(doc) {\n  doc['"+ col +"'] = doc['"+ col +"'];\n  return doc;\n}");
     editor.focus().get(0).setSelectionRange(18, 18);
     editor.keydown();