diff --git a/include/aare/ArrayExpr.hpp b/include/aare/ArrayExpr.hpp
index 7f8015c..d326601 100644
--- a/include/aare/ArrayExpr.hpp
+++ b/include/aare/ArrayExpr.hpp
@@ -1,22 +1,24 @@
 #pragma once
-#include <cstdint> //int64_t
-#include <cstddef> //size_t
+#include <cstdint> 
+#include <cstddef> 
 #include <array> 
-
 #include <cassert>
+#include "aare/defs.hpp"
+
+
 namespace aare {
 
-template <typename E, int64_t Ndim> class ArrayExpr {
+template <typename E, ssize_t Ndim> class ArrayExpr {
   public:
     static constexpr bool is_leaf = false;
 
     auto operator[](size_t i) const { return static_cast<E const &>(*this)[i]; }
     auto operator()(size_t i) const { return static_cast<E const &>(*this)[i]; }
     auto size() const { return static_cast<E const &>(*this).size(); }
-    std::array<int64_t, Ndim> shape() const { return static_cast<E const &>(*this).shape(); }
+    std::array<ssize_t, Ndim> shape() const { return static_cast<E const &>(*this).shape(); }
 };
 
-template <typename A, typename B, int64_t Ndim>
+template <typename A, typename B, ssize_t Ndim>
 class ArrayAdd : public ArrayExpr<ArrayAdd<A, B, Ndim>, Ndim> {
     const A &arr1_;
     const B &arr2_;
@@ -27,10 +29,10 @@ class ArrayAdd : public ArrayExpr<ArrayAdd<A, B, Ndim>, Ndim> {
     }
     auto operator[](int i) const { return arr1_[i] + arr2_[i]; }
     size_t size() const { return arr1_.size(); }
-    std::array<int64_t, Ndim> shape() const { return arr1_.shape(); }
+    std::array<ssize_t, Ndim> shape() const { return arr1_.shape(); }
 };
 
-template <typename A, typename B, int64_t Ndim>
+template <typename A, typename B, ssize_t Ndim>
 class ArraySub : public ArrayExpr<ArraySub<A, B, Ndim>, Ndim> {
     const A &arr1_;
     const B &arr2_;
@@ -41,10 +43,10 @@ class ArraySub : public ArrayExpr<ArraySub<A, B, Ndim>, Ndim> {
     }
     auto operator[](int i) const { return arr1_[i] - arr2_[i]; }
     size_t size() const { return arr1_.size(); }
-    std::array<int64_t, Ndim> shape() const { return arr1_.shape(); }
+    std::array<ssize_t, Ndim> shape() const { return arr1_.shape(); }
 };
 
-template <typename A, typename B, int64_t Ndim>
+template <typename A, typename B, ssize_t Ndim>
 class ArrayMul : public ArrayExpr<ArrayMul<A, B, Ndim>,Ndim> {
     const A &arr1_;
     const B &arr2_;
@@ -55,10 +57,10 @@ class ArrayMul : public ArrayExpr<ArrayMul<A, B, Ndim>,Ndim> {
     }
     auto operator[](int i) const { return arr1_[i] * arr2_[i]; }
     size_t size() const { return arr1_.size(); }
-    std::array<int64_t, Ndim> shape() const { return arr1_.shape(); }
+    std::array<ssize_t, Ndim> shape() const { return arr1_.shape(); }
 };
 
-template <typename A, typename B, int64_t Ndim>
+template <typename A, typename B, ssize_t Ndim>
 class ArrayDiv : public ArrayExpr<ArrayDiv<A, B, Ndim>, Ndim> {
     const A &arr1_;
     const B &arr2_;
@@ -69,27 +71,27 @@ class ArrayDiv : public ArrayExpr<ArrayDiv<A, B, Ndim>, Ndim> {
     }
     auto operator[](int i) const { return arr1_[i] / arr2_[i]; }
     size_t size() const { return arr1_.size(); }
-    std::array<int64_t, Ndim> shape() const { return arr1_.shape(); }
+    std::array<ssize_t, Ndim> shape() const { return arr1_.shape(); }
 };
 
 
 
-template <typename A, typename B, int64_t Ndim>
+template <typename A, typename B, ssize_t Ndim>
 auto operator+(const ArrayExpr<A, Ndim> &arr1, const ArrayExpr<B, Ndim> &arr2) {
     return ArrayAdd<ArrayExpr<A, Ndim>, ArrayExpr<B, Ndim>, Ndim>(arr1, arr2);
 }
 
-template <typename A, typename B, int64_t Ndim>
+template <typename A, typename B, ssize_t Ndim>
 auto operator-(const ArrayExpr<A,Ndim> &arr1, const ArrayExpr<B, Ndim> &arr2) {
     return ArraySub<ArrayExpr<A, Ndim>, ArrayExpr<B, Ndim>, Ndim>(arr1, arr2);
 }
 
-template <typename A, typename B, int64_t Ndim>
+template <typename A, typename B, ssize_t Ndim>
 auto operator*(const ArrayExpr<A, Ndim> &arr1, const ArrayExpr<B, Ndim> &arr2) {
     return ArrayMul<ArrayExpr<A, Ndim>, ArrayExpr<B, Ndim>, Ndim>(arr1, arr2);
 }
 
-template <typename A, typename B, int64_t Ndim>
+template <typename A, typename B, ssize_t Ndim>
 auto operator/(const ArrayExpr<A, Ndim> &arr1, const ArrayExpr<B, Ndim> &arr2) {
     return ArrayDiv<ArrayExpr<A, Ndim>, ArrayExpr<B, Ndim>, Ndim>(arr1, arr2);
 }
diff --git a/include/aare/FilePtr.hpp b/include/aare/FilePtr.hpp
index 4c88ecb..4ddc76e 100644
--- a/include/aare/FilePtr.hpp
+++ b/include/aare/FilePtr.hpp
@@ -18,8 +18,8 @@ class FilePtr {
     FilePtr(FilePtr &&other);
     FilePtr &operator=(FilePtr &&other);
     FILE *get();
-    int64_t tell();
-    void seek(int64_t offset, int whence = SEEK_SET) {
+    ssize_t tell();
+    void seek(ssize_t offset, int whence = SEEK_SET) {
         if (fseek(fp_, offset, whence) != 0)
             throw std::runtime_error("Error seeking in file");
     }
diff --git a/include/aare/Frame.hpp b/include/aare/Frame.hpp
index 5ce63ac..02ea82f 100644
--- a/include/aare/Frame.hpp
+++ b/include/aare/Frame.hpp
@@ -107,8 +107,8 @@ class Frame {
      * @return NDView<T, 2> 
      */
     template <typename T> NDView<T, 2> view() {
-        std::array<int64_t, 2> shape = {static_cast<int64_t>(m_rows),
-                                        static_cast<int64_t>(m_cols)};
+        std::array<ssize_t, 2> shape = {static_cast<ssize_t>(m_rows),
+                                        static_cast<ssize_t>(m_cols)};
         T *data = reinterpret_cast<T *>(m_data);
         return NDView<T, 2>(data, shape);
     }
diff --git a/include/aare/NDArray.hpp b/include/aare/NDArray.hpp
index ceb1e0b..3c08a3c 100644
--- a/include/aare/NDArray.hpp
+++ b/include/aare/NDArray.hpp
@@ -22,10 +22,10 @@ TODO! Add expression templates for operators
 namespace aare {
 
 
-template <typename T, int64_t Ndim = 2>
+template <typename T, ssize_t Ndim = 2>
 class NDArray : public ArrayExpr<NDArray<T, Ndim>, Ndim> {
-    std::array<int64_t, Ndim> shape_;
-    std::array<int64_t, Ndim> strides_;
+    std::array<ssize_t, Ndim> shape_;
+    std::array<ssize_t, Ndim> strides_;
     size_t size_{};
     T *data_;
 
@@ -42,7 +42,7 @@ class NDArray : public ArrayExpr<NDArray<T, Ndim>, Ndim> {
      *
      * @param shape shape of the new NDArray
      */
-    explicit NDArray(std::array<int64_t, Ndim> shape)
+    explicit NDArray(std::array<ssize_t, Ndim> shape)
         : shape_(shape), strides_(c_strides<Ndim>(shape_)),
           size_(std::accumulate(shape_.begin(), shape_.end(), 1,
                                 std::multiplies<>())),
@@ -55,7 +55,7 @@ class NDArray : public ArrayExpr<NDArray<T, Ndim>, Ndim> {
      * @param shape shape of the new array
      * @param value value to initialize the array with
      */
-    NDArray(std::array<int64_t, Ndim> shape, T value) : NDArray(shape) {
+    NDArray(std::array<ssize_t, Ndim> shape, T value) : NDArray(shape) {
         this->operator=(value);
     }
 
@@ -186,22 +186,22 @@ class NDArray : public ArrayExpr<NDArray<T, Ndim>, Ndim> {
     }
 
     // TODO! is int the right type for index?
-    T &operator()(int64_t i) { return data_[i]; }
-    const T &operator()(int64_t i) const { return data_[i]; }
+    T &operator()(ssize_t i) { return data_[i]; }
+    const T &operator()(ssize_t i) const { return data_[i]; }
 
-    T &operator[](int64_t i) { return data_[i]; }
-    const T &operator[](int64_t i) const { return data_[i]; }
+    T &operator[](ssize_t i) { return data_[i]; }
+    const T &operator[](ssize_t i) const { return data_[i]; }
 
     T *data() { return data_; }
     std::byte *buffer() { return reinterpret_cast<std::byte *>(data_); }
     ssize_t size() const { return static_cast<ssize_t>(size_); }
     size_t total_bytes() const { return size_ * sizeof(T); }
-    std::array<int64_t, Ndim> shape() const noexcept { return shape_; }
-    int64_t shape(int64_t i) const noexcept { return shape_[i]; }
-    std::array<int64_t, Ndim> strides() const noexcept { return strides_; }
+    std::array<ssize_t, Ndim> shape() const noexcept { return shape_; }
+    ssize_t shape(ssize_t i) const noexcept { return shape_[i]; }
+    std::array<ssize_t, Ndim> strides() const noexcept { return strides_; }
     size_t bitdepth() const noexcept { return sizeof(T) * 8; }
 
-    std::array<int64_t, Ndim> byte_strides() const noexcept {
+    std::array<ssize_t, Ndim> byte_strides() const noexcept {
         auto byte_strides = strides_;
         for (auto &val : byte_strides)
             val *= sizeof(T);
@@ -228,7 +228,7 @@ class NDArray : public ArrayExpr<NDArray<T, Ndim>, Ndim> {
 };
 
 // Move assign
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> &
 NDArray<T, Ndim>::operator=(NDArray<T, Ndim> &&other) noexcept {
     if (this != &other) {
@@ -242,7 +242,7 @@ NDArray<T, Ndim>::operator=(NDArray<T, Ndim> &&other) noexcept {
     return *this;
 }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> &NDArray<T, Ndim>::operator+=(const NDArray<T, Ndim> &other) {
     // check shape
     if (shape_ == other.shape_) {
@@ -254,7 +254,7 @@ NDArray<T, Ndim> &NDArray<T, Ndim>::operator+=(const NDArray<T, Ndim> &other) {
     throw(std::runtime_error("Shape of ImageDatas must match"));
 }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> &NDArray<T, Ndim>::operator-=(const NDArray<T, Ndim> &other) {
     // check shape
     if (shape_ == other.shape_) {
@@ -266,7 +266,7 @@ NDArray<T, Ndim> &NDArray<T, Ndim>::operator-=(const NDArray<T, Ndim> &other) {
     throw(std::runtime_error("Shape of ImageDatas must match"));
 }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> &NDArray<T, Ndim>::operator*=(const NDArray<T, Ndim> &other) {
     // check shape
     if (shape_ == other.shape_) {
@@ -278,14 +278,14 @@ NDArray<T, Ndim> &NDArray<T, Ndim>::operator*=(const NDArray<T, Ndim> &other) {
     throw(std::runtime_error("Shape of ImageDatas must match"));
 }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> &NDArray<T, Ndim>::operator&=(const T &mask) {
     for (auto it = begin(); it != end(); ++it)
         *it &= mask;
     return *this;
 }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<bool, Ndim> NDArray<T, Ndim>::operator>(const NDArray &other) {
     if (shape_ == other.shape_) {
         NDArray<bool, Ndim> result{shape_};
@@ -297,7 +297,7 @@ NDArray<bool, Ndim> NDArray<T, Ndim>::operator>(const NDArray &other) {
     throw(std::runtime_error("Shape of ImageDatas must match"));
 }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> &NDArray<T, Ndim>::operator=(const NDArray<T, Ndim> &other) {
     if (this != &other) {
         delete[] data_;
@@ -310,7 +310,7 @@ NDArray<T, Ndim> &NDArray<T, Ndim>::operator=(const NDArray<T, Ndim> &other) {
     return *this;
 }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 bool NDArray<T, Ndim>::operator==(const NDArray<T, Ndim> &other) const {
     if (shape_ != other.shape_)
         return false;
@@ -322,23 +322,23 @@ bool NDArray<T, Ndim>::operator==(const NDArray<T, Ndim> &other) const {
     return true;
 }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 bool NDArray<T, Ndim>::operator!=(const NDArray<T, Ndim> &other) const {
     return !((*this) == other);
 }
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> &NDArray<T, Ndim>::operator++() {
     for (uint32_t i = 0; i < size_; ++i)
         data_[i] += 1;
     return *this;
 }
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> &NDArray<T, Ndim>::operator=(const T &value) {
     std::fill_n(data_, size_, value);
     return *this;
 }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> &NDArray<T, Ndim>::operator+=(const T &value) {
     for (uint32_t i = 0; i < size_; ++i)
         data_[i] += value;
@@ -348,57 +348,57 @@ NDArray<T, Ndim> &NDArray<T, Ndim>::operator+=(const T &value) {
 
 
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> NDArray<T, Ndim>::operator+(const T &value) {
     NDArray result = *this;
     result += value;
     return result;
 }
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> &NDArray<T, Ndim>::operator-=(const T &value) {
     for (uint32_t i = 0; i < size_; ++i)
         data_[i] -= value;
     return *this;
 }
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> NDArray<T, Ndim>::operator-(const T &value) {
     NDArray result = *this;
     result -= value;
     return result;
 }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> &NDArray<T, Ndim>::operator/=(const T &value) {
     for (uint32_t i = 0; i < size_; ++i)
         data_[i] /= value;
     return *this;
 }
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> NDArray<T, Ndim>::operator/(const T &value) {
     NDArray result = *this;
     result /= value;
     return result;
 }
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> &NDArray<T, Ndim>::operator*=(const T &value) {
     for (uint32_t i = 0; i < size_; ++i)
         data_[i] *= value;
     return *this;
 }
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> NDArray<T, Ndim>::operator*(const T &value) {
     NDArray result = *this;
     result *= value;
     return result;
 }
-// template <typename T, int64_t Ndim> void NDArray<T, Ndim>::Print() {
+// template <typename T, ssize_t Ndim> void NDArray<T, Ndim>::Print() {
 //     if (shape_[0] < 20 && shape_[1] < 20)
 //         Print_all();
 //     else
 //         Print_some();
 // }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 std::ostream &operator<<(std::ostream &os, const NDArray<T, Ndim> &arr) {
     for (auto row = 0; row < arr.shape(0); ++row) {
         for (auto col = 0; col < arr.shape(1); ++col) {
@@ -410,7 +410,7 @@ std::ostream &operator<<(std::ostream &os, const NDArray<T, Ndim> &arr) {
     return os;
 }
 
-template <typename T, int64_t Ndim> void NDArray<T, Ndim>::Print_all() {
+template <typename T, ssize_t Ndim> void NDArray<T, Ndim>::Print_all() {
     for (auto row = 0; row < shape_[0]; ++row) {
         for (auto col = 0; col < shape_[1]; ++col) {
             std::cout << std::setw(3);
@@ -419,7 +419,7 @@ template <typename T, int64_t Ndim> void NDArray<T, Ndim>::Print_all() {
         std::cout << "\n";
     }
 }
-template <typename T, int64_t Ndim> void NDArray<T, Ndim>::Print_some() {
+template <typename T, ssize_t Ndim> void NDArray<T, Ndim>::Print_some() {
     for (auto row = 0; row < 5; ++row) {
         for (auto col = 0; col < 5; ++col) {
             std::cout << std::setw(7);
@@ -429,7 +429,7 @@ template <typename T, int64_t Ndim> void NDArray<T, Ndim>::Print_some() {
     }
 }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 void save(NDArray<T, Ndim> &img, std::string &pathname) {
     std::ofstream f;
     f.open(pathname, std::ios::binary);
@@ -437,9 +437,9 @@ void save(NDArray<T, Ndim> &img, std::string &pathname) {
     f.close();
 }
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 NDArray<T, Ndim> load(const std::string &pathname,
-                      std::array<int64_t, Ndim> shape) {
+                      std::array<ssize_t, Ndim> shape) {
     NDArray<T, Ndim> img{shape};
     std::ifstream f;
     f.open(pathname, std::ios::binary);
diff --git a/include/aare/NDView.hpp b/include/aare/NDView.hpp
index ddb5d1c..56054e2 100644
--- a/include/aare/NDView.hpp
+++ b/include/aare/NDView.hpp
@@ -14,10 +14,10 @@
 #include <vector>
 namespace aare {
 
-template <int64_t Ndim> using Shape = std::array<int64_t, Ndim>;
+template <ssize_t Ndim> using Shape = std::array<ssize_t, Ndim>;
 
 // TODO! fix mismatch between signed and unsigned
-template <int64_t Ndim> Shape<Ndim> make_shape(const std::vector<size_t> &shape) {
+template <ssize_t Ndim> Shape<Ndim> make_shape(const std::vector<size_t> &shape) {
     if (shape.size() != Ndim)
         throw std::runtime_error("Shape size mismatch");
     Shape<Ndim> arr;
@@ -25,41 +25,41 @@ template <int64_t Ndim> Shape<Ndim> make_shape(const std::vector<size_t> &shape)
     return arr;
 }
 
-template <int64_t Dim = 0, typename Strides> int64_t element_offset(const Strides & /*unused*/) { return 0; }
+template <ssize_t Dim = 0, typename Strides> ssize_t element_offset(const Strides & /*unused*/) { return 0; }
 
-template <int64_t Dim = 0, typename Strides, typename... Ix>
-int64_t element_offset(const Strides &strides, int64_t i, Ix... index) {
+template <ssize_t Dim = 0, typename Strides, typename... Ix>
+ssize_t element_offset(const Strides &strides, ssize_t i, Ix... index) {
     return i * strides[Dim] + element_offset<Dim + 1>(strides, index...);
 }
 
-template <int64_t Ndim> std::array<int64_t, Ndim> c_strides(const std::array<int64_t, Ndim> &shape) {
-    std::array<int64_t, Ndim> strides{};
+template <ssize_t Ndim> std::array<ssize_t, Ndim> c_strides(const std::array<ssize_t, Ndim> &shape) {
+    std::array<ssize_t, Ndim> strides{};
     std::fill(strides.begin(), strides.end(), 1);
-    for (int64_t i = Ndim - 1; i > 0; --i) {
+    for (ssize_t i = Ndim - 1; i > 0; --i) {
         strides[i - 1] = strides[i] * shape[i];
     }
     return strides;
 }
 
-template <int64_t Ndim> std::array<int64_t, Ndim> make_array(const std::vector<int64_t> &vec) {
+template <ssize_t Ndim> std::array<ssize_t, Ndim> make_array(const std::vector<ssize_t> &vec) {
     assert(vec.size() == Ndim);
-    std::array<int64_t, Ndim> arr{};
+    std::array<ssize_t, Ndim> arr{};
     std::copy_n(vec.begin(), Ndim, arr.begin());
     return arr;
 }
 
-template <typename T, int64_t Ndim = 2> class NDView : public ArrayExpr<NDView<T, Ndim>, Ndim> {
+template <typename T, ssize_t Ndim = 2> class NDView : public ArrayExpr<NDView<T, Ndim>, Ndim> {
   public:
     NDView() = default;
     ~NDView() = default;
     NDView(const NDView &) = default;
     NDView(NDView &&) = default;
 
-    NDView(T *buffer, std::array<int64_t, Ndim> shape)
+    NDView(T *buffer, std::array<ssize_t, Ndim> shape)
         : buffer_(buffer), strides_(c_strides<Ndim>(shape)), shape_(shape),
           size_(std::accumulate(std::begin(shape), std::end(shape), 1, std::multiplies<>())) {}
 
-    // NDView(T *buffer, const std::vector<int64_t> &shape)
+    // NDView(T *buffer, const std::vector<ssize_t> &shape)
     //     : buffer_(buffer), strides_(c_strides<Ndim>(make_array<Ndim>(shape))), shape_(make_array<Ndim>(shape)),
     //       size_(std::accumulate(std::begin(shape), std::end(shape), 1, std::multiplies<>())) {}
 
@@ -73,14 +73,14 @@ template <typename T, int64_t Ndim = 2> class NDView : public ArrayExpr<NDView<T
 
     ssize_t size() const { return static_cast<ssize_t>(size_); }
     size_t total_bytes() const { return size_ * sizeof(T); }
-    std::array<int64_t, Ndim> strides() const noexcept { return strides_; }
+    std::array<ssize_t, Ndim> strides() const noexcept { return strides_; }
 
     T *begin() { return buffer_; }
     T *end() { return buffer_ + size_; }
     T const *begin() const { return buffer_; }
     T const *end() const { return buffer_ + size_; }
-    T &operator()(int64_t i) const { return buffer_[i]; }
-    T &operator[](int64_t i) const { return buffer_[i]; }
+    T &operator()(ssize_t i) const { return buffer_[i]; }
+    T &operator[](ssize_t i) const { return buffer_[i]; }
 
     bool operator==(const NDView &other) const {
         if (size_ != other.size_)
@@ -136,15 +136,15 @@ template <typename T, int64_t Ndim = 2> class NDView : public ArrayExpr<NDView<T
     }
 
     auto &shape() const { return shape_; }
-    auto shape(int64_t i) const { return shape_[i]; }
+    auto shape(ssize_t i) const { return shape_[i]; }
 
     T *data() { return buffer_; }
     void print_all() const;
 
   private:
     T *buffer_{nullptr};
-    std::array<int64_t, Ndim> strides_{};
-    std::array<int64_t, Ndim> shape_{};
+    std::array<ssize_t, Ndim> strides_{};
+    std::array<ssize_t, Ndim> shape_{};
     uint64_t size_{};
 
     template <class BinaryOperation> NDView &elemenwise(T val, BinaryOperation op) {
@@ -160,7 +160,7 @@ template <typename T, int64_t Ndim = 2> class NDView : public ArrayExpr<NDView<T
         return *this;
     }
 };
-template <typename T, int64_t Ndim> void NDView<T, Ndim>::print_all() const {
+template <typename T, ssize_t Ndim> void NDView<T, Ndim>::print_all() const {
     for (auto row = 0; row < shape_[0]; ++row) {
         for (auto col = 0; col < shape_[1]; ++col) {
             std::cout << std::setw(3);
@@ -171,7 +171,7 @@ template <typename T, int64_t Ndim> void NDView<T, Ndim>::print_all() const {
 }
 
 
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 std::ostream& operator <<(std::ostream& os, const NDView<T, Ndim>& arr){
     for (auto row = 0; row < arr.shape(0); ++row) {
         for (auto col = 0; col < arr.shape(1); ++col) {
@@ -186,7 +186,7 @@ std::ostream& operator <<(std::ostream& os, const NDView<T, Ndim>& arr){
 
 template <typename T>
 NDView<T,1> make_view(std::vector<T>& vec){
-    return NDView<T,1>(vec.data(), {static_cast<int64_t>(vec.size())});
+    return NDView<T,1>(vec.data(), {static_cast<ssize_t>(vec.size())});
 }
 
 } // namespace aare
\ No newline at end of file
diff --git a/include/aare/NumpyFile.hpp b/include/aare/NumpyFile.hpp
index 9cd2d61..7381a76 100644
--- a/include/aare/NumpyFile.hpp
+++ b/include/aare/NumpyFile.hpp
@@ -69,7 +69,7 @@ class NumpyFile : public FileInterface {
      */
     template <typename T, size_t NDim> NDArray<T, NDim> load() {
         NDArray<T, NDim> arr(make_shape<NDim>(m_header.shape));
-        if (fseek(fp, static_cast<int64_t>(header_size), SEEK_SET)) {
+        if (fseek(fp, static_cast<long>(header_size), SEEK_SET)) {
             throw std::runtime_error(LOCATION + "Error seeking to the start of the data");
         }
         size_t rc = fread(arr.data(), sizeof(T), arr.size(), fp);
diff --git a/include/aare/Pedestal.hpp b/include/aare/Pedestal.hpp
index 102d730..d6223c1 100644
--- a/include/aare/Pedestal.hpp
+++ b/include/aare/Pedestal.hpp
@@ -107,7 +107,7 @@ template <typename SUM_TYPE = double> class Pedestal {
         assert(frame.size() == m_rows * m_cols);
 
         // TODO! move away from m_rows, m_cols
-        if (frame.shape() != std::array<int64_t, 2>{m_rows, m_cols}) {
+        if (frame.shape() != std::array<ssize_t, 2>{m_rows, m_cols}) {
             throw std::runtime_error(
                 "Frame shape does not match pedestal shape");
         }
@@ -128,7 +128,7 @@ template <typename SUM_TYPE = double> class Pedestal {
         assert(frame.size() == m_rows * m_cols);
 
         // TODO! move away from m_rows, m_cols
-        if (frame.shape() != std::array<int64_t, 2>{m_rows, m_cols}) {
+        if (frame.shape() != std::array<ssize_t, 2>{m_rows, m_cols}) {
             throw std::runtime_error(
                 "Frame shape does not match pedestal shape");
         }
diff --git a/include/aare/VarClusterFinder.hpp b/include/aare/VarClusterFinder.hpp
index 161941a..596bf06 100644
--- a/include/aare/VarClusterFinder.hpp
+++ b/include/aare/VarClusterFinder.hpp
@@ -28,7 +28,7 @@ template <typename T> class VarClusterFinder {
     };
 
   private:
-    const std::array<int64_t, 2> shape_;
+    const std::array<ssize_t, 2> shape_;
     NDView<T, 2> original_;
     NDArray<int, 2> labeled_;
     NDArray<int, 2> peripheral_labeled_;
diff --git a/include/aare/defs.hpp b/include/aare/defs.hpp
index 4d22bd4..01d291b 100644
--- a/include/aare/defs.hpp
+++ b/include/aare/defs.hpp
@@ -207,20 +207,20 @@ struct DetectorGeometry{
 };
 
 struct ROI{
-    int64_t xmin{};
-    int64_t xmax{};
-    int64_t ymin{};
-    int64_t ymax{};
+    ssize_t xmin{};
+    ssize_t xmax{};
+    ssize_t ymin{};
+    ssize_t ymax{};
   
-    int64_t height() const { return ymax - ymin; }
-    int64_t width() const { return xmax - xmin; }
-    bool contains(int64_t x, int64_t y) const {
+    ssize_t height() const { return ymax - ymin; }
+    ssize_t width() const { return xmax - xmin; }
+    bool contains(ssize_t x, ssize_t y) const {
         return x >= xmin && x < xmax && y >= ymin && y < ymax;
     }
   };
 
 
-using dynamic_shape = std::vector<int64_t>;
+using dynamic_shape = std::vector<ssize_t>;
 
 //TODO! Can we uniform enums between the libraries?
 
diff --git a/python/src/ctb_raw_file.hpp b/python/src/ctb_raw_file.hpp
index a88a9d1..c9b5310 100644
--- a/python/src/ctb_raw_file.hpp
+++ b/python/src/ctb_raw_file.hpp
@@ -34,7 +34,7 @@ m.def("adc_sar_05_decode64to16", [](py::array_t<uint8_t> input) {
     }
 
     //Create a 2D output array with the same shape as the input
-    std::vector<ssize_t> shape{input.shape(0), input.shape(1)/static_cast<int64_t>(bits_per_byte)};
+    std::vector<ssize_t> shape{input.shape(0), input.shape(1)/static_cast<ssize_t>(bits_per_byte)};
     py::array_t<uint16_t> output(shape);
 
     //Create a view of the input and output arrays
@@ -55,7 +55,7 @@ m.def("adc_sar_04_decode64to16", [](py::array_t<uint8_t> input) {
     }
 
     //Create a 2D output array with the same shape as the input
-    std::vector<ssize_t> shape{input.shape(0), input.shape(1)/static_cast<int64_t>(bits_per_byte)};
+    std::vector<ssize_t> shape{input.shape(0), input.shape(1)/static_cast<ssize_t>(bits_per_byte)};
     py::array_t<uint16_t> output(shape);
 
     //Create a view of the input and output arrays
diff --git a/python/src/file.hpp b/python/src/file.hpp
index 2d0f53e..f97db96 100644
--- a/python/src/file.hpp
+++ b/python/src/file.hpp
@@ -198,7 +198,7 @@ void define_file_io_bindings(py::module &m) {
 
     py::class_<ROI>(m, "ROI")
         .def(py::init<>())
-        .def(py::init<int64_t, int64_t, int64_t, int64_t>(), py::arg("xmin"),
+        .def(py::init<ssize_t, ssize_t, ssize_t, ssize_t>(), py::arg("xmin"),
              py::arg("xmax"), py::arg("ymin"), py::arg("ymax"))
         .def_readwrite("xmin", &ROI::xmin)
         .def_readwrite("xmax", &ROI::xmax)
diff --git a/python/src/np_helper.hpp b/python/src/np_helper.hpp
index 3d3ee3c..78166aa 100644
--- a/python/src/np_helper.hpp
+++ b/python/src/np_helper.hpp
@@ -13,7 +13,7 @@ namespace py = pybind11;
 using namespace aare;
 
 // Pass image data back to python as a numpy array
-template <typename T, int64_t Ndim>
+template <typename T, ssize_t Ndim>
 py::array return_image_data(aare::NDArray<T, Ndim> *image) {
 
     py::capsule free_when_done(image, [](void *f) {
diff --git a/src/FilePtr.cpp b/src/FilePtr.cpp
index 4fed3d7..e3cdb4b 100644
--- a/src/FilePtr.cpp
+++ b/src/FilePtr.cpp
@@ -21,7 +21,7 @@ FilePtr &FilePtr::operator=(FilePtr &&other) {
 
 FILE *FilePtr::get() { return fp_; }
 
-int64_t FilePtr::tell() {
+ssize_t FilePtr::tell() {
     auto pos = ftell(fp_);
     if (pos == -1)
         throw std::runtime_error(fmt::format("Error getting file position: {}", error_msg()));
diff --git a/src/NDArray.test.cpp b/src/NDArray.test.cpp
index c37a285..819a1a9 100644
--- a/src/NDArray.test.cpp
+++ b/src/NDArray.test.cpp
@@ -44,9 +44,9 @@ TEST_CASE("3D NDArray from NDView"){
     REQUIRE(image.size() == view.size());
     REQUIRE(image.data() != view.data());
 
-    for(int64_t i=0; i<image.shape(0); i++){
-        for(int64_t j=0; j<image.shape(1); j++){
-            for(int64_t k=0; k<image.shape(2); k++){
+    for(ssize_t i=0; i<image.shape(0); i++){
+        for(ssize_t j=0; j<image.shape(1); j++){
+            for(ssize_t k=0; k<image.shape(2); k++){
                 REQUIRE(image(i, j, k) == view(i, j, k));
             }
         }
@@ -54,7 +54,7 @@ TEST_CASE("3D NDArray from NDView"){
 }
 
 TEST_CASE("1D image") {
-    std::array<int64_t, 1> shape{{20}};
+    std::array<ssize_t, 1> shape{{20}};
     NDArray<short, 1> img(shape, 3);
     REQUIRE(img.size() == 20);
     REQUIRE(img(5) == 3);
@@ -71,7 +71,7 @@ TEST_CASE("Accessing a const object") {
 }
 
 TEST_CASE("Indexing of a 2D image") {
-    std::array<int64_t, 2> shape{{3, 7}};
+    std::array<ssize_t, 2> shape{{3, 7}};
     NDArray<long> img(shape, 5);
     for (uint32_t i = 0; i != img.size(); ++i) {
         REQUIRE(img(i) == 5);
@@ -114,7 +114,7 @@ TEST_CASE("Divide double by int") {
 }
 
 TEST_CASE("Elementwise multiplication of 3D image") {
-    std::array<int64_t, 3> shape{3, 4, 2};
+    std::array<ssize_t, 3> shape{3, 4, 2};
     NDArray<double, 3> a{shape};
     NDArray<double, 3> b{shape};
     for (uint32_t i = 0; i != a.size(); ++i) {
@@ -179,9 +179,9 @@ TEST_CASE("Compare two images") {
 }
 
 TEST_CASE("Size and shape matches") {
-    int64_t w = 15;
-    int64_t h = 75;
-    std::array<int64_t, 2> shape{w, h};
+    ssize_t w = 15;
+    ssize_t h = 75;
+    std::array<ssize_t, 2> shape{w, h};
     NDArray<double> a{shape};
     REQUIRE(a.size() == w * h);
     REQUIRE(a.shape() == shape);
@@ -224,7 +224,7 @@ TEST_CASE("Bitwise and on data") {
 
 
 TEST_CASE("Elementwise operations on images") {
-    std::array<int64_t, 2> shape{5, 5};
+    std::array<ssize_t, 2> shape{5, 5};
     double a_val = 3.0;
     double b_val = 8.0;
 
diff --git a/src/NDView.test.cpp b/src/NDView.test.cpp
index 8750f3a..89e76e9 100644
--- a/src/NDView.test.cpp
+++ b/src/NDView.test.cpp
@@ -142,7 +142,7 @@ TEST_CASE("iterators") {
 //     for (int i = 0; i != 12; ++i) {
 //         vec.push_back(i);
 //     }
-//     std::vector<int64_t> shape{3, 4};
+//     std::vector<ssize_t> shape{3, 4};
 //     NDView<int, 2> data(vec.data(), shape);
 // }
 
@@ -151,8 +151,8 @@ TEST_CASE("divide with another span") {
     std::vector<int> vec1{3, 2, 1};
     std::vector<int> result{3, 6, 3};
 
-    NDView<int, 1> data0(vec0.data(), Shape<1>{static_cast<int64_t>(vec0.size())});
-    NDView<int, 1> data1(vec1.data(), Shape<1>{static_cast<int64_t>(vec1.size())});
+    NDView<int, 1> data0(vec0.data(), Shape<1>{static_cast<ssize_t>(vec0.size())});
+    NDView<int, 1> data1(vec1.data(), Shape<1>{static_cast<ssize_t>(vec1.size())});
 
     data0 /= data1;
 
diff --git a/src/decode.cpp b/src/decode.cpp
index 8ac7bc0..436ad7b 100644
--- a/src/decode.cpp
+++ b/src/decode.cpp
@@ -26,8 +26,8 @@ void adc_sar_05_decode64to16(NDView<uint64_t, 2> input, NDView<uint16_t,2> outpu
         throw std::invalid_argument(LOCATION + " input and output shapes must match");
     }
 
-    for(int64_t i = 0; i < input.shape(0); i++){
-        for(int64_t j = 0; j < input.shape(1); j++){
+    for(ssize_t i = 0; i < input.shape(0); i++){
+        for(ssize_t j = 0; j < input.shape(1); j++){
             output(i,j) = adc_sar_05_decode64to16(input(i,j));
         }
     }
@@ -56,8 +56,8 @@ void adc_sar_04_decode64to16(NDView<uint64_t, 2> input, NDView<uint16_t,2> outpu
     if(input.shape() != output.shape()){
         throw std::invalid_argument(LOCATION + " input and output shapes must match");
     }
-    for(int64_t i = 0; i < input.shape(0); i++){
-        for(int64_t j = 0; j < input.shape(1); j++){
+    for(ssize_t i = 0; i < input.shape(0); i++){
+        for(ssize_t j = 0; j < input.shape(1); j++){
             output(i,j) = adc_sar_04_decode64to16(input(i,j));
         }
     }