diff --git a/nixos/neovim.nix b/nixos/neovim.nix
index b820bdf..90743fb 100644
--- a/nixos/neovim.nix
+++ b/nixos/neovim.nix
@@ -45,6 +45,16 @@
       vim.opt.spell = true
       vim.opt.spelllang = "en_us"
 
+      -- Markdown: fold by heading/section using Treesitter
+      vim.api.nvim_create_autocmd("FileType", {
+        pattern = "markdown",
+        callback = function()
+          vim.opt_local.foldmethod = "expr"
+          vim.opt_local.foldexpr = "v:lua.vim.treesitter.foldexpr()"
+          vim.opt_local.foldenable = true
+        end,
+      })
+
       -- Keymaps
       vim.keymap.set("n", "S", ":%s//g<Left><Left>", { desc = "Replace all" })
       vim.keymap.set("n", "<leader>w", ":w<CR>", { desc = "Save file" })