diff --git a/src/pyj/popups.pyj b/src/pyj/popups.pyj
index af2095e21c..1f78f13cf3 100644
--- a/src/pyj/popups.pyj
+++ b/src/pyj/popups.pyj
@@ -45,7 +45,9 @@ def create_popup(parent, idprefix):
     nonlocal popup_count
     popup_count += 1
     pid = (idprefix or 'popup') + '-' + popup_count
-    div = E.div(id=pid, style='display: none; position: absolute; z-index: {}'.format(POPUP_Z_INDEX))
+    # Position has to be fixed so that setting style.top/style.bottom works in
+    # viewport co-ordinates
+    div = E.div(id=pid, style='display: none; position: fixed; z-index: {}'.format(POPUP_Z_INDEX))
     parent = parent or document.body
     parent.appendChild(div)
     return div
@@ -166,7 +168,7 @@ class CompletionPopup:
         cs = c.style
         cs.left = x + 'px'
         cs.top = 'auto' if upwards else y + 'px'
-        cs.bottom = y + 'px' if upwards else 'auto'
+        cs.bottom = (window.innerHeight - y) + 'px' if upwards else 'auto'
         cs.width = width + 'px'
         cs.maxHeight = ((y if upwards else window.innerHeight - y) - 10) + 'px'
         show_popup(self.container_id, self.associated_widget_ids)