diff --git a/djangocms_snippet/forms.py b/djangocms_snippet/forms.py
index 64337d95..e503b9d5 100644
--- a/djangocms_snippet/forms.py
+++ b/djangocms_snippet/forms.py
@@ -28,8 +28,9 @@ class Meta:
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
-        self.fields["snippet_grouper"].required = False
-        self.fields["snippet_grouper"].widget = forms.HiddenInput()
+        if self.fields.get("snippet_grouper"):
+            self.fields["snippet_grouper"].required = False
+            self.fields["snippet_grouper"].widget = forms.HiddenInput()
 
     def clean(self):
         data = super().clean()
diff --git a/tests/test_admin.py b/tests/test_admin.py
index 69fe4d50..54d37120 100644
--- a/tests/test_admin.py
+++ b/tests/test_admin.py
@@ -97,3 +97,19 @@ def test_admin_form_save_method(self):
         # We should have 2 groupers and snippets, due to the creation of the others in setUp
         self.assertEqual(Snippet._base_manager.count(), 2)
         self.assertEqual(SnippetGrouper._base_manager.count(), 2)
+
+    @override_settings(DJANGOCMS_SNIPPET_VERSIONING_ENABLED=True)
+    def test_admin_form_edit_when_locked(self):
+        """
+        When a form is initialised in read-only mode, it should not require self.fields to be populated, and
+        should return a read-only form.
+        """
+        self.snippet_version.publish(user=self.superuser)
+        with self.login_user_context(self.superuser):
+            edit_url = reverse("admin:djangocms_snippet_snippet_change", args=(self.snippet.id,),)
+            response = self.client.get(edit_url)
+
+        # Check that we are loading in readonly mode
+        self.assertContains(response, '<div class="readonly">Test Snippet</div>')
+        # We should have the same number of snippets as before
+        self.assertEqual(Snippet.objects.count(), 1)