diff --git a/src/script/api/script_group.cpp b/src/script/api/script_group.cpp
--- a/src/script/api/script_group.cpp
+++ b/src/script/api/script_group.cpp
@@ -111,7 +111,10 @@
 /* static */ SQInteger ScriptGroup::GetNumEngines(GroupID group_id, EngineID engine_id)
 {
 	EnforceCompanyModeValid(-1);
-	if (!IsValidGroup(group_id) && group_id != GROUP_DEFAULT && group_id != GROUP_ALL) return -1;
+	if (!ScriptEngine::IsValidEngine(engine_id)) return -1;
+	bool valid_group = IsValidGroup(group_id);
+	if (!valid_group && group_id != GROUP_DEFAULT && group_id != GROUP_ALL) return -1;
+	if (valid_group && ScriptEngine::GetVehicleType(engine_id) != GetVehicleType(group_id)) return -1;
 
 	return GetGroupNumEngines(ScriptObject::GetCompany(), group_id, engine_id);
 }