diff --git a/runtime/lua/vim/filetype.lua b/runtime/lua/vim/filetype.lua
index e954ef036c..bacbf17ab2 100644
--- a/runtime/lua/vim/filetype.lua
+++ b/runtime/lua/vim/filetype.lua
@@ -330,6 +330,7 @@ local extension = {
   cbl = 'cobol',
   atg = 'coco',
   recipe = 'conaryrecipe',
+  cto = 'concerto',
   ctags = 'conf',
   hook = function(_path, bufnr)
     return M._getline(bufnr, 1) == '[Trigger]' and 'confini' or nil
diff --git a/test/old/testdir/test_filetype.vim b/test/old/testdir/test_filetype.vim
index 3dbc3b55fd..0902c78334 100644
--- a/test/old/testdir/test_filetype.vim
+++ b/test/old/testdir/test_filetype.vim
@@ -194,6 +194,7 @@ func s:GetFilenameChecks() abort
     \ 'coco': ['file.atg'],
     \ 'codeowners': ['CODEOWNERS'],
     \ 'conaryrecipe': ['file.recipe'],
+    \ 'concerto': ['file.cto'],
     \ 'conf': ['auto.master', 'file.conf', 'texdoc.cnf', '.x11vncrc', '.chktexrc', '.ripgreprc', 'ripgreprc', 'file.ctags'],
     \ 'config': ['/etc/hostname.file', 'any/etc/hostname.file', 'configure.in', 'configure.ac', 'file.at', 'aclocal.m4'],
     \ 'confini': ['pacman.conf', 'paru.conf', 'mpv.conf', 'any/.aws/config', 'any/.aws/credentials', 'any/.aws/cli/alias', 'file.nmconnection',