diff --git a/modules/completion/nvim-cmp/config.nix b/modules/completion/nvim-cmp/config.nix
index 72c9a1a..8ad7336 100644
--- a/modules/completion/nvim-cmp/config.nix
+++ b/modules/completion/nvim-cmp/config.nix
@@ -200,12 +200,13 @@ in {
 
       local cmp = require'cmp'
       cmp.setup({
+        ${optionalString (config.vim.ui.borders.enable) ''
+        -- explicitly enabled by setting ui.borders.enable = true
         window = {
-          -- TODO: at some point, those need to be optional
-          -- but first nvim cmp module needs to be detached from "cfg.autocomplete"
           completion = cmp.config.window.bordered(),
           documentation = cmp.config.window.bordered(),
         },
+      ''}
 
         snippet = {
           expand = function(args)
diff --git a/modules/lsp/lspconfig/config.nix b/modules/lsp/lspconfig/config.nix
index 70485be..cdcadc8 100644
--- a/modules/lsp/lspconfig/config.nix
+++ b/modules/lsp/lspconfig/config.nix
@@ -16,6 +16,11 @@ in {
 
       vim.luaConfigRC.lspconfig = nvim.dag.entryAfter ["lsp-setup"] ''
         local lspconfig = require('lspconfig')
+
+        ${
+          # TODO: make border style configurable
+          optionalString (config.vim.ui.borders.enable) "require('lspconfig.ui.windows').default_options.border = 'single'"
+        }
       '';
     }
     {
diff --git a/modules/ui/borders/borders.nix b/modules/ui/borders/borders.nix
new file mode 100644
index 0000000..b11d2cd
--- /dev/null
+++ b/modules/ui/borders/borders.nix
@@ -0,0 +1,9 @@
+{lib, ...}: let
+  inherit (lib) mkEnableOption mkOption;
+in {
+  options.vim.ui.borders = {
+    enable = mkEnableOption "visible borders for most windows";
+
+    # TODO: make per-plugin borders configurable
+  };
+}
diff --git a/modules/ui/borders/default.nix b/modules/ui/borders/default.nix
new file mode 100644
index 0000000..526ac4e
--- /dev/null
+++ b/modules/ui/borders/default.nix
@@ -0,0 +1,5 @@
+_: {
+  imports = [
+    ./borders.nix
+  ];
+}
diff --git a/modules/ui/default.nix b/modules/ui/default.nix
index 980a04a..757dd46 100644
--- a/modules/ui/default.nix
+++ b/modules/ui/default.nix
@@ -6,5 +6,6 @@ _: {
     ./smartcolumn
     ./colorizer
     ./illuminate
+    ./borders
   ];
 }