diff --git a/Eigen/src/SparseCore/SparseMatrix.h b/Eigen/src/SparseCore/SparseMatrix.h
index 4c8965802..4562f3df9 100644
--- a/Eigen/src/SparseCore/SparseMatrix.h
+++ b/Eigen/src/SparseCore/SparseMatrix.h
@@ -467,6 +467,8 @@ class SparseMatrix
       if(isCompressed())
         return;
       
+      eigen_internal_assert(m_outerIndex!=0 && m_outerSize>0);
+      
       Index oldStart = m_outerIndex[1];
       m_outerIndex[1] = m_innerNonZeros[0];
       for(Index j=1; j<m_outerSize; ++j)