diff --git a/cmake/modules/FindEigen3.cmake b/cmake/modules/FindEigen3.cmake
index fe82bb9f..e33a2678 100644
--- a/cmake/modules/FindEigen3.cmake
+++ b/cmake/modules/FindEigen3.cmake
@@ -49,7 +49,18 @@ if(NOT Eigen3_FIND_VERSION)
 endif()
 
 macro(_eigen3_check_version)
-  file(READ "${EIGEN3_INCLUDE_DIR}/Eigen/src/Core/util/Macros.h" _eigen3_version_header)
+  # Try the Eigen 5.x location first
+  if(EXISTS "${EIGEN3_INCLUDE_DIR}/Eigen/Version")
+    file(READ "${EIGEN3_INCLUDE_DIR}/Eigen/Version" _eigen3_version_header)
+  # Fall back to Eigen 3.x location
+  elseif(EXISTS "${EIGEN3_INCLUDE_DIR}/Eigen/src/Core/util/Macros.h")
+    file(READ "${EIGEN3_INCLUDE_DIR}/Eigen/src/Core/util/Macros.h" _eigen3_version_header)
+  else()
+    # Could not locate any known Eigen version header; mark version as not OK and return.
+    set(EIGEN3_VERSION_OK FALSE)
+    message(STATUS "Could not find Eigen version header under ${EIGEN3_INCLUDE_DIR}")
+    return()
+  endif()
 
   string(REGEX MATCH "define[ \t]+EIGEN_WORLD_VERSION[ \t]+([0-9]+)" _eigen3_world_version_match "${_eigen3_version_header}")
   set(EIGEN3_WORLD_VERSION "${CMAKE_MATCH_1}")
diff --git a/export/CMakeLists.txt.export b/export/CMakeLists.txt.export
index 3c28edb4..45fb1a78 100644
--- a/export/CMakeLists.txt.export
+++ b/export/CMakeLists.txt.export
@@ -172,7 +172,7 @@ find_package(Eigen3 MODULE)
 if (TARGET Eigen3::Eigen)
     set(LIBINT_HAS_EIGEN 1)
 endif()
-if (LIBINT2_REQUIRE_CXX_API AND NOT ${LIBINT_HAS_EIGEN})
+if (LIBINT2_REQUIRE_CXX_API AND NOT LIBINT_HAS_EIGEN)
     message(FATAL_ERROR "C++ API cannot be built without Eigen3; configure (via CMake) and install Eigen3 and add the install prefix to CMAKE_PREFIX_PATH, or add -D LIBINT2_REQUIRE_CXX_API=OFF to the CMake command line if the C++ API is not required")
 endif()