diff --git a/unsupported/Eigen/AutoDiff b/unsupported/Eigen/AutoDiff
index 1d1be3b67..62fc0b34e 100644
--- a/unsupported/Eigen/AutoDiff
+++ b/unsupported/Eigen/AutoDiff
@@ -10,6 +10,8 @@
 #ifndef EIGEN_AUTODIFF_MODULE_H
 #define EIGEN_AUTODIFF_MODULE_H
 
+#include "../../Eigen/Core"
+
 namespace Eigen {
 
 /**