diff --git a/lib/awful/prompt.lua b/lib/awful/prompt.lua
index 91b745a04..13ec58a90 100644
--- a/lib/awful/prompt.lua
+++ b/lib/awful/prompt.lua
@@ -18,6 +18,7 @@ local capi =
 {
     selection = selection
 }
+local unpack = unpack or table.unpack -- luacheck: globals unpack (compatibility with Lua 5.1)
 local keygrabber = require("awful.keygrabber")
 local util = require("awful.util")
 local beautiful = require("beautiful")