diff --git a/lua/lean/widget/interactive_code.lua b/lua/lean/widget/interactive_code.lua
index b3dae4ef..2bce87df 100644
--- a/lua/lean/widget/interactive_code.lua
+++ b/lua/lean/widget/interactive_code.lua
@@ -64,7 +64,7 @@ local function render_subexpr_info(subexpr_info, tag, sess, locations, self_rend
       tooltip_element:add_child(InteractiveCode(info_popup.type, sess, locations))
     end
 
-    if info_popup.doc ~= nil then
+    if type(info_popup.doc) == 'string' then
       tooltip_element:add_child(Element:new { text = '\n\n' })
       tooltip_element:add_child(Element:new { text = info_popup.doc }) -- TODO: markdown
     end