diff --git a/unittest/tensor.cpp b/unittest/tensor.cpp
index e50caf2f5ccce5eaddf2f96d1f1bbc8ac8bf3327..c770112b3f26c9e65c960f8faf9e9b65c10057e6 100644
--- a/unittest/tensor.cpp
+++ b/unittest/tensor.cpp
@@ -126,7 +126,7 @@ struct TensorContainer {
 
   Tensor m_tensor;
   TensorContainer(const Dimensions& dims) {
-    typedef Eigen::array<long, Rank> InternalDimension;
+    typedef Eigen::array<typename Tensor::Index, Rank> InternalDimension;
     InternalDimension _dims;
     for (size_t k = 0; k < Rank; ++k) _dims[k] = dims[Eigen::DenseIndex(k)];