diff --git a/runtime/lua/vim/filetype/detect.lua b/runtime/lua/vim/filetype/detect.lua
index 45244af64c..16c3c43446 100644
--- a/runtime/lua/vim/filetype/detect.lua
+++ b/runtime/lua/vim/filetype/detect.lua
@@ -908,9 +908,13 @@ function M.ll(_, bufnr)
   local first_line = getline(bufnr, 1)
   if matchregex(first_line, [[;\|\<source_filename\>\|\<target\>]]) then
     return 'llvm'
-  else
-    return 'lifelines'
   end
+  for _, line in ipairs(getlines(bufnr, 1, 100)) do
+    if line:find('^%s*%%') then
+      return 'lex'
+    end
+  end
+  return 'lifelines'
 end
 
 --- @type vim.filetype.mapfn
diff --git a/test/old/testdir/test_filetype.vim b/test/old/testdir/test_filetype.vim
index 760afc2e85..81dcb9a570 100644
--- a/test/old/testdir/test_filetype.vim
+++ b/test/old/testdir/test_filetype.vim
@@ -2600,6 +2600,12 @@ func Test_ll_file()
   call assert_equal('llvm', &filetype)
   bwipe!
 
+  " lex (C++)
+  call writefile(['%{', '#include <iostream>', '%}'], 'Xfile.ll', 'D')
+  split Xfile.ll
+  call assert_equal('lex', &filetype)
+  bwipe!
+
   " lifelines
   call writefile(['proc main() {}'], 'Xfile.ll', 'D')
   split Xfile.ll