diff --git a/tex/generic/pgf/systemlayer/pgfsys.code.tex b/tex/generic/pgf/systemlayer/pgfsys.code.tex
index a67329729..0c99fb830 100644
--- a/tex/generic/pgf/systemlayer/pgfsys.code.tex
+++ b/tex/generic/pgf/systemlayer/pgfsys.code.tex
@@ -1725,7 +1725,8 @@
 \else\ifdefined\directlua
   \directlua{
   local lft = lua.get_functions_table()
-  lft[\string#lft+1] = function()
+  local fid = luatexbase and luatexbase.new_luafunction("pgfsys@strcmp") or \string#lft+1
+  lft[fid] = function()
       local lhs = token.scan_string()
       local rhs = token.scan_string()
       if lhs < rhs then
@@ -1736,7 +1737,7 @@
           tex.sprint(-2, "1")
       end
   end
-  token.set_lua("pgfsys@strcmp", \string#lft, "global")
+  token.set_lua("pgfsys@strcmp", fid, "global")
   }
 \else
   \def\pgfsys@strcmp#1#2{\pgf@sys@fail{string comparison}}%