diff --git a/src/obj.js b/src/obj.js
index c2dc720d9..df09d3630 100644
--- a/src/obj.js
+++ b/src/obj.js
@@ -342,8 +342,9 @@ var XRef = (function XRefClosure() {
 
     var encrypt = trailerDict.get('Encrypt');
     if (encrypt) {
-      var fileId = trailerDict.get('ID');
-      this.encrypt = new CipherTransformFactory(encrypt, fileId[0], password);
+      var ids = trailerDict.get('ID');
+      var fileId = (ids && ids.length) ? ids[0] : '';
+      this.encrypt = new CipherTransformFactory(encrypt, fileId, password);
     }
 
     // get the root dictionary (catalog) object