diff -up luaposix-release-v33.3.1/ext/include/_helpers.c.54 luaposix-release-v33.3.1/ext/include/_helpers.c
--- luaposix-release-v33.3.1/ext/include/_helpers.c.54	2020-06-29 23:52:30.433291702 -0400
+++ luaposix-release-v33.3.1/ext/include/_helpers.c	2020-06-29 23:52:53.714914130 -0400
@@ -67,7 +67,7 @@
 #  endif
 #endif
 
-#if LUA_VERSION_NUM == 502 || LUA_VERSION_NUM == 503
+#if LUA_VERSION_NUM == 502 || LUA_VERSION_NUM == 503 || LUA_VERSION_NUM == 504
 #  define lua_objlen lua_rawlen
 #  define lua_strlen lua_rawlen
 #  define luaL_openlib(L,n,l,nup) luaL_setfuncs((L),(l),(nup))