diff --git a/qutebrowser/models/completionfilter.py b/qutebrowser/models/completionfilter.py
index ba2e1e057..a294e4800 100644
--- a/qutebrowser/models/completionfilter.py
+++ b/qutebrowser/models/completionfilter.py
@@ -72,11 +72,17 @@ class CompletionFilterModel(QSortFilterProxyModel):
 
     def first_item(self):
         """Return the first item in the model."""
+        # FIXME if the tree looks like this:
+        # - cat1
+        # + cat2
+        #    - item
+        # then this will yield an invalid index.
         cat = self.index(0, 0)
         return self.index(0, 0, cat)
 
     def last_item(self):
         """Return the last item in the model."""
+        # FIXME this has about the same problem as above
         cat = self.index(self.rowCount() - 1, 0)
         return self.index(self.rowCount(cat) - 1, 0, cat)