diff --git a/src/nvim/lua/executor.c b/src/nvim/lua/executor.c
index 4e017d23be..ef0d6d0dc9 100644
--- a/src/nvim/lua/executor.c
+++ b/src/nvim/lua/executor.c
@@ -277,16 +277,18 @@ lua_State *get_global_lstate(void)
 /// The returned string points to memory on the Lua stack. Use or duplicate it before using
 /// `lstate` again.
 ///
-/// @param[out] len length of error (can be NULL)
+/// @param[out] len length of error
 static const char *nlua_get_error(lua_State *lstate, size_t *len)
+  FUNC_ATTR_NONNULL_RET
 {
-  if (luaL_getmetafield(lstate, -1, "__tostring")) {
-    if (lua_isfunction(lstate, -1) && luaL_callmeta(lstate, -2, "__tostring")) {
-      // call __tostring, convert the result and replace error with it
-      lua_replace(lstate, -3);
+  if (lua_type(lstate, -1) != LUA_TSTRING) {
+    lua_getglobal(lstate, "tostring");
+    lua_pushvalue(lstate, -2);
+    if (lua_pcall(lstate, 1, 1, 0) || lua_type(lstate, -1) != LUA_TSTRING) {
+      lua_pop(lstate, 1);
+      lua_pushstring(lstate, "[UNPRINTABLE ERROR]");
     }
-    // pop __tostring.
-    lua_pop(lstate, 1);
+    lua_replace(lstate, -2);
   }
 
   return lua_tolstring(lstate, -1, len);
@@ -433,10 +435,11 @@ static int nlua_luv_thread_common_cfpcall(lua_State *lstate, int nargs, int nres
       pthread_exit(0);
 #endif
     }
-    const char *error = lua_tostring(lstate, -1);
+    size_t len;
+    const char *error = nlua_get_error(lstate, &len);
     loop_schedule_deferred(&main_loop,
                            event_create(nlua_luv_error_event,
-                                        error != NULL ? xstrdup(error) : NULL,
+                                        xmemdupz(error, len),
                                         (void *)(intptr_t)(is_callback
                                                            ? kThreadCallback
                                                            : kThread)));
diff --git a/test/functional/api/command_spec.lua b/test/functional/api/command_spec.lua
index d5a83015bc..c1eb1f92c3 100644
--- a/test/functional/api/command_spec.lua
+++ b/test/functional/api/command_spec.lua
@@ -828,7 +828,7 @@ describe('nvim_create_user_command', function()
       })
     ]])
     feed(':Test <Tab>')
-    eq('E5108: Lua function: [NULL]', api.nvim_get_vvar('errmsg'))
+    eq('E5108: Lua function: nil', api.nvim_get_vvar('errmsg'))
     eq('Test ', fn.getcmdline())
     assert_alive()
   end)
diff --git a/test/functional/lua/commands_spec.lua b/test/functional/lua/commands_spec.lua
index 0bfb9f006f..70ac8f2e7c 100644
--- a/test/functional/lua/commands_spec.lua
+++ b/test/functional/lua/commands_spec.lua
@@ -72,8 +72,22 @@ describe(':lua', function()
     eq({ '' }, api.nvim_buf_get_lines(0, 0, 100, false))
   end)
 
-  it('works with NULL errors', function()
-    eq([=[Vim(lua):E5108: Lua: [NULL]]=], pcall_err(command, 'lua error(nil)'))
+  it('works with nil errors', function()
+    eq([=[Vim(lua):E5108: Lua: nil]=], pcall_err(command, 'lua error(nil)'))
+  end)
+
+  it('works with errors with __tostring failure', function()
+    eq(
+      [=[Vim(lua):E5108: Lua: [UNPRINTABLE ERROR]]=],
+      pcall_err(command, 'lua error(setmetatable({}, {__tostring=error}))')
+    )
+  end)
+
+  it('works with printable errors', function()
+    eq([=[Vim(lua):E5108: Lua: false]=], pcall_err(command, 'lua error(false)'))
+    -- numbers get the location prefixed because numbers are almost strings (know the workplace rules)
+    eq([=[Vim(lua):E5108: Lua: [string ":lua"]:0: 39]=], pcall_err(command, 'lua error(39)'))
+    matches([=[Vim%(lua%):E5108: Lua: table: 0x%x+]=], pcall_err(command, 'lua error({})'))
   end)
 
   it('accepts embedded NLs without heredoc', function()
@@ -280,8 +294,8 @@ describe(':luado command', function()
     )
   end)
 
-  it('works with NULL errors', function()
-    eq([=[Vim(luado):E5111: Lua: [NULL]]=], pcall_err(command, 'luado error(nil)'))
+  it('works with nil errors', function()
+    eq([=[Vim(luado):E5111: Lua: nil]=], pcall_err(command, 'luado error(nil)'))
   end)
 
   it('fails in sandbox when needed', function()
@@ -342,8 +356,8 @@ describe(':luafile', function()
     )
   end)
 
-  it('works with NULL errors', function()
+  it('works with nil errors', function()
     write_file(fname, 'error(nil)')
-    eq([=[Vim(luafile):E5113: Lua chunk: [NULL]]=], pcall_err(command, 'luafile ' .. fname))
+    eq([=[Vim(luafile):E5113: Lua chunk: nil]=], pcall_err(command, 'luafile ' .. fname))
   end)
 end)
diff --git a/test/functional/lua/luaeval_spec.lua b/test/functional/lua/luaeval_spec.lua
index 1eb8cf9958..e4591a3a60 100644
--- a/test/functional/lua/luaeval_spec.lua
+++ b/test/functional/lua/luaeval_spec.lua
@@ -495,7 +495,7 @@ describe('luaeval()', function()
       remove_trace(pcall_err(command, [[call luaeval("error('ERROR')")]]))
     )
     eq(
-      'Vim(call):E5108: Lua: [NULL]',
+      'Vim(call):E5108: Lua: nil',
       remove_trace(pcall_err(command, [[call luaeval("error(nil)")]]))
     )
   end)
diff --git a/test/functional/lua/overrides_spec.lua b/test/functional/lua/overrides_spec.lua
index e0d0bd908e..def1f7ae73 100644
--- a/test/functional/lua/overrides_spec.lua
+++ b/test/functional/lua/overrides_spec.lua
@@ -4,6 +4,7 @@ local n = require('test.functional.testnvim')()
 local Screen = require('test.functional.ui.screen')
 
 local eq = t.eq
+local matches = t.matches
 local NIL = vim.NIL
 local feed = n.feed
 local clear = n.clear
@@ -105,13 +106,13 @@ describe('print', function()
       'Vim(lua):E5108: Lua: Xtest-functional-lua-overrides-luafile:2: 1234',
       pcall_err(command, 'lua number_error()')
     )
-    eq('Vim(lua):E5108: Lua: [NULL]', pcall_err(command, 'lua nil_error()'))
-    eq('Vim(lua):E5108: Lua: [NULL]', pcall_err(command, 'lua table_error()'))
+    eq('Vim(lua):E5108: Lua: nil', pcall_err(command, 'lua nil_error()'))
+    matches('^Vim%(lua%):E5108: Lua: table: 0x%x+$', pcall_err(command, 'lua table_error()'))
     eq(
       'Vim(lua):E5108: Lua: Internal Error [11234] my mistake',
       pcall_err(command, 'lua custom_error()')
     )
-    eq('Vim(lua):E5108: Lua: [NULL]', pcall_err(command, 'lua bad_custom_error()'))
+    eq('Vim(lua):E5108: Lua: [UNPRINTABLE ERROR]', pcall_err(command, 'lua bad_custom_error()'))
   end)
   it('prints strings with NULs and NLs correctly', function()
     api.nvim_set_option_value('more', true, {})
diff --git a/test/functional/lua/thread_spec.lua b/test/functional/lua/thread_spec.lua
index e4ff2b8068..1232b3843d 100644
--- a/test/functional/lua/thread_spec.lua
+++ b/test/functional/lua/thread_spec.lua
@@ -32,7 +32,7 @@ describe('thread', function()
       {1:~                                                 }|*5
       {3:                                                  }|
       {9:Luv thread:}                                       |
-      {9:[NULL]}                                            |
+      {9:nil}                                               |
       {6:Press ENTER or type command to continue}^           |
     ]])
     feed('<cr>')
diff --git a/test/functional/lua/uv_spec.lua b/test/functional/lua/uv_spec.lua
index 848a073cb5..7c865da54f 100644
--- a/test/functional/lua/uv_spec.lua
+++ b/test/functional/lua/uv_spec.lua
@@ -174,7 +174,7 @@ describe('vim.uv', function()
       {1:~                                                 }|*5
       {3:                                                  }|
       {9:Lua callback:}                                     |
-      {9:[NULL]}                                            |
+      {9:nil}                                               |
       {6:Press ENTER or type command to continue}^           |
     ]]
     screen:expect(s)
@@ -209,7 +209,7 @@ describe('vim.uv', function()
     screen:expect([[
       {3:                                                  }|
       {9:Lua callback:}                                     |
-      {9:[NULL]}                                            |
+      {9:nil}                                               |
       {6:Press ENTER or type command to continue}^           |
     ]])
     feed('<cr>')