diff --git a/pkgs/development/interpreters/lua-5/setup-hook.sh b/pkgs/development/interpreters/lua-5/setup-hook.sh
index f7e56b62ac90..1c445b82afde 100644
--- a/pkgs/development/interpreters/lua-5/setup-hook.sh
+++ b/pkgs/development/interpreters/lua-5/setup-hook.sh
@@ -20,7 +20,7 @@ addToLuaSearchPathWithCustomDelimiter() {
   if [[ ! -d "$topDir" ]]; then return; fi
 
   # export only if we haven't already got this dir in the search path
-  if [[ ${!varName} == *"$absPattern"* ]]; then return; fi
+  if [[ ${!varName-} == *"$absPattern"* ]]; then return; fi
 
   export "${varName}=${!varName:+${!varName};}${absPattern}"
 }