diff --git a/test/functional/plugin/pack_spec.lua b/test/functional/plugin/pack_spec.lua
index bc28b026b3..af85487e6e 100644
--- a/test/functional/plugin/pack_spec.lua
+++ b/test/functional/plugin/pack_spec.lua
@@ -983,6 +983,7 @@ describe('vim.pack', function()
         local fetch_path = pack_get_plug_path('fetch')
         local semver_src = repos_src.semver
         local semver_path = pack_get_plug_path('semver')
+        local pack_runtime = '/lua/vim/pack.lua'
 
         exec_lua(function()
           -- Replace matches in line to preserve extmark highlighting
@@ -998,10 +999,11 @@ describe('vim.pack', function()
 
           vim.bo.modifiable = true
           local lines = vim.api.nvim_buf_get_lines(0, 0, -1, false)
-          local pack_runtime = vim.fs.joinpath(vim.env.VIMRUNTIME, 'lua', 'vim', 'pack.lua')
           -- NOTE: replace path to `vim.pack` in error traceback accounting for
-          -- possibly different slashes on Windows
-          local pack_runtime_pattern = vim.pesc(pack_runtime):gsub('/', '[\\/]') .. ':%d+'
+          -- pcall source truncation and possibly different slashes on Windows
+          local pack_runtime_pattern = ('%%S.+%s:%%d+'):format(
+            vim.pesc(pack_runtime):gsub('/', '[\\/]')
+          )
           for i = 1, #lines do
             replace_in_line(i, pack_runtime_pattern, 'VIM_PACK_RUNTIME')
             replace_in_line(i, vim.pesc(fetch_path), 'FETCH_PATH')