diff --git a/tests/backoffice_pages/test_submission.py b/tests/backoffice_pages/test_submission.py
index 8d1bf9fb2..818b17332 100644
--- a/tests/backoffice_pages/test_submission.py
+++ b/tests/backoffice_pages/test_submission.py
@@ -1687,7 +1687,13 @@ def test_backoffice_submission_user_selection_then_live_prefill(pub):
     assert resp.pyquery('.submit-user-selection')
     resp.form['user_id'] = str(random_user.id)  # happens via javascript
     live_resp = app.post(live_url + '?modified_field_id=user', params=resp.form.submit_fields())
-    assert live_resp.json == {'result': {'3': {'visible': True, 'content': 'test9@invalid'}}}
+    assert live_resp.json == {'result': {'3': {'visible': True, 'content': 'test9@invalid', 'locked': False}}}
+
+    # check with locked field
+    formdef.fields[1].prefill['locked'] = True
+    formdef.store()
+    live_resp = app.post(live_url + '?modified_field_id=user', params=resp.form.submit_fields())
+    assert live_resp.json == {'result': {'3': {'visible': True, 'content': 'test9@invalid', 'locked': True}}}
 
 
 def test_backoffice_submission_user_selection_then_card_data_source(pub):
diff --git a/wcs/forms/common.py b/wcs/forms/common.py
index 24ffea75e..018eb78ef 100644
--- a/wcs/forms/common.py
+++ b/wcs/forms/common.py
@@ -948,8 +948,9 @@ class FormStatusPage(Directory, FormTemplateMixin):
             elif field.get_prefill_configuration().get('type') == 'user':
                 update_prefill = bool(get_request().form.get('modified_field_id') == 'user')
                 if update_prefill:
-                    value = field.get_prefill_value(user=formdata.user)[0]
+                    value, locked = field.get_prefill_value(user=formdata.user)
                     entry['content'] = value
+                    entry['locked'] = locked
 
         return json.dumps({'result': result})
 
diff --git a/wcs/qommon/static/js/qommon.forms.js b/wcs/qommon/static/js/qommon.forms.js
index e35fa0d46..cecfd7674 100644
--- a/wcs/qommon/static/js/qommon.forms.js
+++ b/wcs/qommon/static/js/qommon.forms.js
@@ -611,6 +611,10 @@ $(function() {
                     $(widget).find('input[type=radio]').prop('checked', false);
                     $(widget).find('input[type=radio][value="'+value.content+'"]').prop('checked', true);
                   }
+                  if (data.modified_field == 'user' && value.locked) {
+                    $(widget).addClass('widget-readonly');
+                    $(widget).find('input').attr('readonly', 'readonly');
+                  }
                 }
               }
             });