diff --git a/app/assets/javascripts/editor/submissions.js.erb b/app/assets/javascripts/editor/submissions.js.erb
index 08e62dba..e860c7a6 100644
--- a/app/assets/javascripts/editor/submissions.js.erb
+++ b/app/assets/javascripts/editor/submissions.js.erb
@@ -54,8 +54,8 @@ CodeOceanEditorSubmissions = {
       // This is the case, since it is set via a call to ancestor_id on the model, which returns either file_id if set, or id if it is not set.
       // therefore the else part is not needed any longer...
 
-      // if we have an file_id set (the file is a copy of a teacher supplied given file)
-      if (file_id_old != null){
+      // if we have an file_id set (the file is a copy of a teacher supplied given file) and the new file-ids are present in the response
+      if (file_id_old != null && data.files){
         // if we find file_id_old (this is the reference to the base file) in the submission, this is the match
         for(var j = 0; j< data.files.length; j++){
           if(data.files[j].file_id == file_id_old){