diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorFFT.h b/unsupported/Eigen/CXX11/src/Tensor/TensorFFT.h
index 3bfaf6d23..9e675ad0f 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorFFT.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorFFT.h
@@ -206,7 +206,7 @@ struct TensorEvaluator<const TensorFFTOp<FFT, ArgType, FFTResultType, FFTDir>, D
     }
 
     for (size_t i = 0; i < m_fft.size(); ++i) {
-      int dim = m_fft[i];
+      Index dim = m_fft[i];
       eigen_assert(dim >= 0 && dim < NumDims);
       Index line_len = m_dimensions[dim];
       eigen_assert(line_len >= 1);
diff --git a/unsupported/test/cxx11_tensor_fft.cpp b/unsupported/test/cxx11_tensor_fft.cpp
index b2a4b5a96..89874349f 100644
--- a/unsupported/test/cxx11_tensor_fft.cpp
+++ b/unsupported/test/cxx11_tensor_fft.cpp
@@ -192,7 +192,7 @@ static void test_fft_real_input_energy() {
   input.resize(arr);
   input.setRandom();
 
-  array<int, TensorRank> fft;
+  array<ptrdiff_t, TensorRank> fft;
   for (int i = 0; i < TensorRank; ++i) {
     fft[i] = i;
   }