diff --git a/src/atlas/interpolation/method/sphericalvector/ComplexMatrixMultiply.h b/src/atlas/interpolation/method/sphericalvector/ComplexMatrixMultiply.h
index d9812ba97..05253f9f1 100644
--- a/src/atlas/interpolation/method/sphericalvector/ComplexMatrixMultiply.h
+++ b/src/atlas/interpolation/method/sphericalvector/ComplexMatrixMultiply.h
@@ -58,7 +58,7 @@ class ComplexMatrixMultiply {
       ATLAS_ASSERT(complexWeightsPtr_->cols() == realWeightsPtr_->cols());
       ATLAS_ASSERT(complexWeightsPtr_->nonZeros() ==
                    realWeightsPtr_->nonZeros());
-      for (auto rowIndex = Size{0}; rowIndex < complexWeightsPtr_->rows();
+      for (auto rowIndex = Index{0}; rowIndex < complexWeightsPtr_->rows();
            ++rowIndex) {
         for (auto [complexRowIter, realRowIter] = rowIters(rowIndex);
              complexRowIter; ++complexRowIter, ++realRowIter) {
@@ -100,7 +100,7 @@ class ComplexMatrixMultiply {
     // We could probably optimise contiguous arrays using
     // reinterpret_cast<std::complex<double>*>(view.data()). This is fine
     // according to the C++ standard!
-    atlas_omp_parallel_for(auto rowIndex = Size{0};
+    atlas_omp_parallel_for(auto rowIndex = Index{0};
                            rowIndex < complexWeightsPtr_->rows(); ++rowIndex) {
       auto targetSlice = sliceColumn(targetView, rowIndex);
       if constexpr (InitialiseTarget) {
@@ -129,7 +129,7 @@ class ComplexMatrixMultiply {
   template <typename Value, int Rank>
   void applyThreeVector(const array::ArrayView<const Value, Rank>& sourceView,
                         array::ArrayView<Value, Rank>& targetView) const {
-    atlas_omp_parallel_for(auto rowIndex = Size{0};
+    atlas_omp_parallel_for(auto rowIndex = Index{0};
                            rowIndex < complexWeightsPtr_->rows(); ++rowIndex) {
       auto targetSlice = sliceColumn(targetView, rowIndex);
       if constexpr (InitialiseTarget) {
@@ -158,7 +158,7 @@ class ComplexMatrixMultiply {
 
   /// @brief Return a pair of complex and real row iterators
   std::pair<ComplexMatrix::RowIter, RealMatrix::RowIter> rowIters(
-      Size rowIndex) const {
+      Index rowIndex) const {
     return std::make_pair(complexWeightsPtr_->rowIter(rowIndex),
                           realWeightsPtr_->rowIter(rowIndex));
   }
diff --git a/src/atlas/interpolation/method/sphericalvector/SparseMatrix.h b/src/atlas/interpolation/method/sphericalvector/SparseMatrix.h
index 4f5c079e6..4b0786559 100644
--- a/src/atlas/interpolation/method/sphericalvector/SparseMatrix.h
+++ b/src/atlas/interpolation/method/sphericalvector/SparseMatrix.h
@@ -17,6 +17,7 @@
 #endif
 
 #include "atlas/runtime/Exception.h"
+#include "eckit/log/CodeLocation.h"
 
 namespace atlas {
 namespace interpolation {
@@ -31,12 +32,10 @@ namespace detail {
 ///          class is Eigen library is not present.
 template <typename Value>
 class SparseMatrix {
-  using EigenMatrix = Eigen::SparseMatrix<Value, Eigen::RowMajor>;
-
  public:
-  using Index = typename EigenMatrix::StorageIndex;
-  using Size = typename EigenMatrix::Index;
-  using Triplet = Eigen::Triplet<Value>;
+  using Index = int;
+  using EigenMatrix = Eigen::SparseMatrix<Value, Eigen::RowMajor, Index>;
+  using Triplet = Eigen::Triplet<Value, Index>;
   using Triplets = std::vector<Triplet>;
   using RowIter = typename EigenMatrix::InnerIterator;
 
@@ -45,10 +44,10 @@ class SparseMatrix {
     eigenMatrix_.setFromTriplets(triplets.begin(), triplets.end());
   }
 
-  Size nonZeros() const { return eigenMatrix_.nonZeros(); }
-  Size rows() const { return eigenMatrix_.rows(); }
-  Size cols() const { return eigenMatrix_.cols(); }
-  RowIter rowIter(Size rowIndex) const {
+  Index nonZeros() const { return eigenMatrix_.nonZeros(); }
+  Index rows() const { return eigenMatrix_.rows(); }
+  Index cols() const { return eigenMatrix_.cols(); }
+  RowIter rowIter(Index rowIndex) const {
     return RowIter(eigenMatrix_, rowIndex);
   }
   SparseMatrix<Value> adjoint() const {
@@ -66,7 +65,6 @@ template <typename Value>
 class SparseMatrix {
  public:
   using Index = int;
-  using Size = long int;
 
   class Triplet {
    public:
@@ -90,10 +88,10 @@ class SparseMatrix {
   SparseMatrix(const Args&... args) {
     throw_Exception("Atlas has been compiled without Eigen", Here());
   }
-  constexpr Size nonZeros() const { return Size{}; }
-  constexpr Size rows() const { return Size{}; }
-  constexpr Size cols() const { return Size{}; }
-  constexpr RowIter rowIter(Size rowIndex) const { return RowIter{}; }
+  constexpr Index nonZeros() const { return Index{}; }
+  constexpr Index rows() const { return Index{}; }
+  constexpr Index cols() const { return Index{}; }
+  constexpr RowIter rowIter(Index rowIndex) const { return RowIter{}; }
   constexpr SparseMatrix<Value> adjoint() const {
     return SparseMatrix<Value>{};
   }
diff --git a/src/atlas/interpolation/method/sphericalvector/SphericalVector.cc b/src/atlas/interpolation/method/sphericalvector/SphericalVector.cc
index 2efd610b3..410f19a01 100644
--- a/src/atlas/interpolation/method/sphericalvector/SphericalVector.cc
+++ b/src/atlas/interpolation/method/sphericalvector/SphericalVector.cc
@@ -34,6 +34,8 @@ using namespace detail;
 
 SphericalVector::SphericalVector(const Config& config) : Method(config) {
   const auto& conf = dynamic_cast<const eckit::LocalConfiguration&>(config);
+  ATLAS_ASSERT_MSG(&conf,
+                   "config must be castable to an eckit::LocalConfiguration");
   interpolationScheme_ = conf.getSubConfiguration("scheme");
   adjoint_ = conf.getBool("adjoint", false);
 }
@@ -56,9 +58,9 @@ void SphericalVector::do_setup(const FunctionSpace& source,
   setMatrix(Interpolation(interpolationScheme_, source_, target_));
 
   // Get matrix data.
-  const auto nRows = matrix().rows();
-  const auto nCols = matrix().cols();
-  const auto nNonZeros = matrix().nonZeros();
+  const auto nRows = static_cast<Index>(matrix().rows());
+  const auto nCols = static_cast<Index>(matrix().cols());
+  const auto nNonZeros = static_cast<std::size_t>(matrix().nonZeros());
   const auto* outerIndices = matrix().outer();
   const auto* innerIndices = matrix().inner();
   const auto* baseWeights = matrix().data();
@@ -87,7 +89,7 @@ void SphericalVector::do_setup(const FunctionSpace& source,
                          ++rowIndex) {
     for (auto dataIndex = outerIndices[rowIndex];
          dataIndex < outerIndices[rowIndex + 1]; ++dataIndex) {
-      const auto colIndex = innerIndices[dataIndex];
+      const auto colIndex = static_cast<Index>(innerIndices[dataIndex]);
       const auto baseWeight = baseWeights[dataIndex];
 
       const auto sourceLonLat = PointLonLat(sourceLonLatsView(colIndex, 0),
diff --git a/src/atlas/interpolation/method/sphericalvector/Types.h b/src/atlas/interpolation/method/sphericalvector/Types.h
index 8ad44092a..fcffc26c8 100644
--- a/src/atlas/interpolation/method/sphericalvector/Types.h
+++ b/src/atlas/interpolation/method/sphericalvector/Types.h
@@ -22,7 +22,6 @@ using Complex = std::complex<Real>;
 using ComplexMatrix = SparseMatrix<Complex>;
 using RealMatrix = SparseMatrix<Real>;
 using Index = ComplexMatrix::Index;
-using Size = ComplexMatrix::Size;
 using ComplexTriplet = ComplexMatrix::Triplet;
 using ComplexTriplets = ComplexMatrix::Triplets;
 using RealTriplet = RealMatrix::Triplet;