diff --git a/Eigen/src/SparseCore/SparseVector.h b/Eigen/src/SparseCore/SparseVector.h
index e027c5d01..8be6144ba 100644
--- a/Eigen/src/SparseCore/SparseVector.h
+++ b/Eigen/src/SparseCore/SparseVector.h
@@ -347,6 +347,7 @@ class SparseVector<Scalar,_Options,_Index>::InnerIterator
     InnerIterator(const SparseVector& vec, Index outer=0)
       : m_data(vec.m_data), m_id(0), m_end(static_cast<Index>(m_data.size()))
     {
+      EIGEN_UNUSED_VARIABLE(outer);
       eigen_assert(outer==0);
     }