diff --git a/src/script/squirrel.cpp b/src/script/squirrel.cpp
index f5550acb82..3e4abc5e79 100644
--- a/src/script/squirrel.cpp
+++ b/src/script/squirrel.cpp
@@ -511,6 +511,7 @@ bool Squirrel::CreateClassInstance(const std::string &class_name, void *real_ins
 
 /* static */ SQUserPointer Squirrel::GetRealInstance(HSQUIRRELVM vm, int index, const char *tag)
 {
+	if (index < 0) index += sq_gettop(vm) + 1;
 	Squirrel *engine = static_cast<Squirrel *>(sq_getforeignptr(vm));
 	std::string class_name = fmt::format("{}{}", engine->GetAPIName(), tag);
 	sq_pushroottable(vm);