--- CMakeLists.txt.orig	2024-02-12 18:24:36 UTC
+++ CMakeLists.txt
@@ -1,5 +1,7 @@ cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
 cmake_minimum_required(VERSION 3.3 FATAL_ERROR)
 
+find_package (Eigen3 3.3 REQUIRED NO_MODULE)
+
 if (NOT TARGET Avogadro::Core)
   find_package(AvogadroLibs REQUIRED)
 endif()