diff --git a/Eigen/Sparse b/Eigen/Sparse
index ce6ef2f3c..bdc45610d 100644
--- a/Eigen/Sparse
+++ b/Eigen/Sparse
@@ -11,6 +11,10 @@
 #include <cstring>
 #include <algorithm>
 
+#ifndef EIGEN_YES_I_KNOW_SPARSE_MODULE_IS_NOT_STABLE_YET
+#error The sparse module API is not stable yet. To use it anyway, please define the EIGEN_YES_I_KNOW_SPARSE_MODULE_IS_NOT_STABLE_YET preprocessor token.
+#endif
+
 namespace Eigen {
 
 /** \defgroup Sparse_Module Sparse module
diff --git a/test/sparse.h b/test/sparse.h
index 1489f2a0e..b343427e5 100644
--- a/test/sparse.h
+++ b/test/sparse.h
@@ -24,6 +24,8 @@
 
 #ifndef EIGEN_TESTSPARSE_H
 
+#define EIGEN_YES_I_KNOW_SPARSE_MODULE_IS_NOT_STABLE_YET
+
 #include "main.h"
 
 #if EIGEN_GNUC_AT_LEAST(4,0) && !defined __ICC