diff --git a/rc/base/lua.kak b/rc/base/lua.kak
index a1454759..ef8cfbdf 100644
--- a/rc/base/lua.kak
+++ b/rc/base/lua.kak
@@ -11,7 +11,7 @@ hook global BufSetOption mimetype=text/x-lua %{
 }
 
 hook global BufCreate .*[.](lua) %{
-    set buffer filetype lua
+    set buffer mimetype text/x-lua
 }
 
 # Highlighters
@@ -32,6 +32,31 @@ addhl -group /lua/code regex \<(and|break|do|else|elseif|end|false|for|function|
 # Commands
 # ‾‾‾‾‾‾‾‾
 
+def lua-alternative-file -docstring 'Jump to the alternate file (implementation ↔ test)' %{ %sh{
+    case $kak_buffile in
+        *spec/*_spec.lua)
+            altfile=$(eval echo $(echo $kak_buffile | sed -e s+spec/+'*'/+';'s/_spec//))
+            [ ! -f $altfile ] && echo "echo -color Error 'implementation file not found'" && exit
+        ;;
+        *.lua)
+            path=$kak_buffile
+            dirs=$(while [ $path ]; do echo $path; path=${path%/*}; done | tail -n +2)
+            for dir in $dirs; do
+                altdir=$dir/spec
+                if [ -d $altdir ]; then
+                    altfile=$altdir/$(realpath $kak_buffile --relative-to $dir | sed -e s+[^/]'*'/++';'s/.lua$/_spec.lua/)
+                    break
+                fi
+            done
+            [ ! -d $altdir ] && echo "echo -color Error 'spec/ not found'" && exit
+        ;;
+        *)
+            echo "echo -color Error 'alternative file not found'" && exit
+        ;;
+    esac
+    echo "edit $altfile"
+}}
+
 def -hidden _lua_filter_around_selections %{
     eval -draft -itersel %{
         exec <a-x>
@@ -77,6 +102,8 @@ hook global WinSetOption filetype=lua %{
     hook window InsertChar .* -group lua-indent _lua_indent_on_char
     hook window InsertChar \n -group lua-indent _lua_indent_on_new_line
 
+    alias window alt lua-alternative-file
+
     set window comment_line_chars '--'
     set window comment_selection_chars '\Q--[[:]]'
 }
@@ -85,4 +112,6 @@ hook global WinSetOption filetype=(?!lua).* %{
     rmhl lua
     rmhooks window lua-indent
     rmhooks window lua-hooks
+
+    unalias window alt lua-alternative-file
 }