diff --git a/src/script/common/c_internal.h b/src/script/common/c_internal.h
index ecb514c8f..80576b5e9 100644
--- a/src/script/common/c_internal.h
+++ b/src/script/common/c_internal.h
@@ -34,6 +34,27 @@ extern "C" {
 
 #include "common/c_types.h"
 
+
+/*
+	Define our custom indices into the Lua registry table.
+
+	Lua 5.2 and above define the LUA_RIDX_LAST macro. Only numbers above that
+	may be used for custom indices, anything else is reserved.
+
+	Lua 5.1 / LuaJIT do not use any numeric indices (only string indices),
+	so we can use numeric indices freely.
+*/
+#ifdef LUA_RIDX_LAST
+#define CUSTOM_RIDX_BASE ((LUA_RIDX_LAST)+1)
+#else
+#define CUSTOM_RIDX_BASE 1
+#endif
+
+#define CUSTOM_RIDX_SCRIPTAPI           (CUSTOM_RIDX_BASE)
+#define CUSTOM_RIDX_GLOBALS_BACKUP      (CUSTOM_RIDX_BASE + 1)
+#define CUSTOM_RIDX_CURRENT_MOD_NAME    (CUSTOM_RIDX_BASE + 2)
+
+
 #define PCALL_RESL(L, RES) do {                         \
 	int result_ = (RES);                                \
 	if (result_ != 0) {                                 \
diff --git a/src/script/cpp_api/s_base.cpp b/src/script/cpp_api/s_base.cpp
index dcfbac4bf..bfe03ec46 100644
--- a/src/script/cpp_api/s_base.cpp
+++ b/src/script/cpp_api/s_base.cpp
@@ -52,13 +52,13 @@ public:
 	{
 		// Store current mod name in registry
 		lua_pushstring(L, mod_name.c_str());
-		lua_setfield(L, LUA_REGISTRYINDEX, SCRIPT_MOD_NAME_FIELD);
+		lua_rawseti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_CURRENT_MOD_NAME);
 	}
 	~ModNameStorer()
 	{
 		// Clear current mod name from registry
 		lua_pushnil(L);
-		lua_setfield(L, LUA_REGISTRYINDEX, SCRIPT_MOD_NAME_FIELD);
+		lua_rawseti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_CURRENT_MOD_NAME);
 	}
 };
 
@@ -84,7 +84,7 @@ ScriptApiBase::ScriptApiBase()
 
 	// Make the ScriptApiBase* accessible to ModApiBase
 	lua_pushlightuserdata(m_luastack, this);
-	lua_setfield(m_luastack, LUA_REGISTRYINDEX, "scriptapi");
+	lua_rawseti(m_luastack, LUA_REGISTRYINDEX, CUSTOM_RIDX_SCRIPTAPI);
 
 	// If we are using LuaJIT add a C++ wrapper function to catch
 	// exceptions thrown in Lua -> C++ calls
diff --git a/src/script/cpp_api/s_base.h b/src/script/cpp_api/s_base.h
index 744fca2d0..b686d7747 100644
--- a/src/script/cpp_api/s_base.h
+++ b/src/script/cpp_api/s_base.h
@@ -36,7 +36,6 @@ extern "C" {
 #define SCRIPTAPI_LOCK_DEBUG
 #define SCRIPTAPI_DEBUG
 
-#define SCRIPT_MOD_NAME_FIELD "current_mod_name"
 // MUST be an invalid mod name so that mods can't
 // use that name to bypass security!
 #define BUILTIN_MOD_NAME "*builtin*"
diff --git a/src/script/cpp_api/s_security.cpp b/src/script/cpp_api/s_security.cpp
index 6a6d40307..36f8e9c0d 100644
--- a/src/script/cpp_api/s_security.cpp
+++ b/src/script/cpp_api/s_security.cpp
@@ -47,7 +47,7 @@ static inline void copy_safe(lua_State *L, const char *list[], unsigned len, int
 // Pushes the original version of a library function on the stack, from the old version
 static inline void push_original(lua_State *L, const char *lib, const char *func)
 {
-	lua_getfield(L, LUA_REGISTRYINDEX, "globals_backup");
+	lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_GLOBALS_BACKUP);
 	lua_getfield(L, -1, lib);
 	lua_remove(L, -2);  // Remove globals_backup
 	lua_getfield(L, -1, func);
@@ -143,7 +143,7 @@ void ScriptApiSecurity::initializeSecurity()
 
 	// Backup globals to the registry
 	lua_getglobal(L, "_G");
-	lua_setfield(L, LUA_REGISTRYINDEX, "globals_backup");
+	lua_rawseti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_GLOBALS_BACKUP);
 
 	// Replace the global environment with an empty one
 #if LUA_VERSION_NUM <= 501
@@ -165,7 +165,7 @@ void ScriptApiSecurity::initializeSecurity()
 #endif
 
 	// Get old globals
-	lua_getfield(L, LUA_REGISTRYINDEX, "globals_backup");
+	lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_GLOBALS_BACKUP);
 	int old_globals = lua_gettop(L);
 
 
@@ -241,7 +241,7 @@ void ScriptApiSecurity::initializeSecurity()
 
 bool ScriptApiSecurity::isSecure(lua_State *L)
 {
-	lua_getfield(L, LUA_REGISTRYINDEX, "globals_backup");
+	lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_GLOBALS_BACKUP);
 	bool secure = !lua_isnil(L, -1);
 	lua_pop(L, 1);
 	return secure;
@@ -356,7 +356,7 @@ bool ScriptApiSecurity::checkPath(lua_State *L, const char *path)
 	if (!removed.empty()) abs_path += DIR_DELIM + removed;
 
 	// Get server from registry
-	lua_getfield(L, LUA_REGISTRYINDEX, "scriptapi");
+	lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_SCRIPTAPI);
 	ScriptApiBase *script = (ScriptApiBase *) lua_touserdata(L, -1);
 	lua_pop(L, 1);
 	const Server *server = script->getServer();
@@ -364,7 +364,7 @@ bool ScriptApiSecurity::checkPath(lua_State *L, const char *path)
 	if (!server) return false;
 
 	// Get mod name
-	lua_getfield(L, LUA_REGISTRYINDEX, SCRIPT_MOD_NAME_FIELD);
+	lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_CURRENT_MOD_NAME);
 	if (lua_isstring(L, -1)) {
 		std::string mod_name = lua_tostring(L, -1);
 
diff --git a/src/script/lua_api/l_base.cpp b/src/script/lua_api/l_base.cpp
index 6ad3e4ba2..515a7d933 100644
--- a/src/script/lua_api/l_base.cpp
+++ b/src/script/lua_api/l_base.cpp
@@ -26,7 +26,7 @@ with this program; if not, write to the Free Software Foundation, Inc.,
 ScriptApiBase *ModApiBase::getScriptApiBase(lua_State *L)
 {
 	// Get server from registry
-	lua_getfield(L, LUA_REGISTRYINDEX, "scriptapi");
+	lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_SCRIPTAPI);
 	ScriptApiBase *sapi_ptr = (ScriptApiBase*) lua_touserdata(L, -1);
 	lua_pop(L, 1);
 	return sapi_ptr;
@@ -49,7 +49,7 @@ GUIEngine *ModApiBase::getGuiEngine(lua_State *L)
 
 std::string ModApiBase::getCurrentModPath(lua_State *L)
 {
-	lua_getfield(L, LUA_REGISTRYINDEX, SCRIPT_MOD_NAME_FIELD);
+	lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_CURRENT_MOD_NAME);
 	const char *current_mod_name = lua_tostring(L, -1);
 	if (!current_mod_name)
 		return ".";
diff --git a/src/script/lua_api/l_server.cpp b/src/script/lua_api/l_server.cpp
index 73eca9d60..a6dac487b 100644
--- a/src/script/lua_api/l_server.cpp
+++ b/src/script/lua_api/l_server.cpp
@@ -345,7 +345,7 @@ int ModApiServer::l_show_formspec(lua_State *L)
 int ModApiServer::l_get_current_modname(lua_State *L)
 {
 	NO_MAP_LOCK_REQUIRED;
-	lua_getfield(L, LUA_REGISTRYINDEX, SCRIPT_MOD_NAME_FIELD);
+	lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_CURRENT_MOD_NAME);
 	return 1;
 }
 
@@ -442,7 +442,7 @@ int ModApiServer::l_notify_authentication_modified(lua_State *L)
 int ModApiServer::l_get_last_run_mod(lua_State *L)
 {
 	NO_MAP_LOCK_REQUIRED;
-	lua_getfield(L, LUA_REGISTRYINDEX, SCRIPT_MOD_NAME_FIELD);
+	lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_CURRENT_MOD_NAME);
 	const char *current_mod = lua_tostring(L, -1);
 	if (current_mod == NULL || current_mod[0] == '\0') {
 		lua_pop(L, 1);
diff --git a/src/script/lua_api/l_util.cpp b/src/script/lua_api/l_util.cpp
index 12146e80a..4b8b6d351 100644
--- a/src/script/lua_api/l_util.cpp
+++ b/src/script/lua_api/l_util.cpp
@@ -371,7 +371,7 @@ int ModApiUtil::l_request_insecure_environment(lua_State *L)
 		lua_getglobal(L, "_G");
 		return 1;
 	}
-	lua_getfield(L, LUA_REGISTRYINDEX, SCRIPT_MOD_NAME_FIELD);
+	lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_CURRENT_MOD_NAME);
 	if (!lua_isstring(L, -1)) {
 		lua_pushnil(L);
 		return 1;
@@ -383,7 +383,7 @@ int ModApiUtil::l_request_insecure_environment(lua_State *L)
 		lua_pushnil(L);
 		return 1;
 	}
-	lua_getfield(L, LUA_REGISTRYINDEX, "globals_backup");
+	lua_rawgeti(L, LUA_REGISTRYINDEX, CUSTOM_RIDX_GLOBALS_BACKUP);
 	return 1;
 }