diff --git a/13/CMakeLists.txt b/13/CMakeLists.txt
index 8a3f3c1..851c568 100644
--- a/13/CMakeLists.txt
+++ b/13/CMakeLists.txt
@@ -1,6 +1,10 @@
 cmake_minimum_required(VERSION 3.1)
 project(compiler)
 
+# We want C++17 for std::optional
+set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
 # Find all the required packages
 find_package(BISON)
 find_package(FLEX)