diff --git a/deps_src/eigen/CMakeLists.txt b/deps_src/eigen/CMakeLists.txt
index b534a55d825..c0cb27d3ae2 100644
--- a/deps_src/eigen/CMakeLists.txt
+++ b/deps_src/eigen/CMakeLists.txt
@@ -1,12 +1,36 @@
 cmake_minimum_required(VERSION 3.13)
 project(eigen)
 
-# Use the pre-built Eigen from deps/ (Eigen3Config.cmake is installed there via CMAKE_PREFIX_PATH).
-# The bundled headers in this directory are an older version and must not be used directly,
-# as libigl and admesh require Eigen3::Eigen with Eigen 3.4+ features (e.g. Eigen::all).
-find_package(Eigen3 REQUIRED NO_MODULE)
+# Try to find the pre-built Eigen3 installed by deps/ CMakeLists (Eigen 5.x).
+# This must succeed: libigl and admesh use Eigen 3.4+ features (e.g. Eigen::all).
+find_package(Eigen3 CONFIG QUIET)
 
-# Provide a plain "eigen" alias for any code that links to the unnamespaced target.
+if(Eigen3_FOUND OR TARGET Eigen3::Eigen)
+    message(STATUS "deps_src/eigen: using pre-built Eigen3 from CMAKE_PREFIX_PATH")
+else()
+    # Fall back: construct the include path from the known deps install location.
+    # CMAKE_PREFIX_PATH points to deps/build/OrcaSlicer_dep/usr/local;
+    # Eigen installs its headers under <prefix>/include/eigen3.
+    set(_eigen_include "")
+    foreach(_prefix ${CMAKE_PREFIX_PATH})
+        if(EXISTS "${_prefix}/include/eigen3")
+            set(_eigen_include "${_prefix}/include/eigen3")
+            break()
+        endif()
+    endforeach()
+
+    if(_eigen_include)
+        message(STATUS "deps_src/eigen: using eigen3 headers from ${_eigen_include}")
+        add_library(Eigen3::Eigen INTERFACE IMPORTED GLOBAL)
+        set_target_properties(Eigen3::Eigen PROPERTIES
+            INTERFACE_INCLUDE_DIRECTORIES "${_eigen_include}")
+    else()
+        message(FATAL_ERROR "deps_src/eigen: could not locate Eigen3 headers. "
+            "Ensure deps/ has been built first (cmake --build deps/build).")
+    endif()
+endif()
+
+# Provide unnamespaced "eigen" alias for targets that link against it directly.
 if(NOT TARGET eigen)
     add_library(eigen INTERFACE)
     target_link_libraries(eigen INTERFACE Eigen3::Eigen)