diff --git a/core/file/json_utils.cpp b/core/file/json_utils.cpp
index 20cd367da3..a6b42c0ffa 100644
--- a/core/file/json_utils.cpp
+++ b/core/file/json_utils.cpp
@@ -14,6 +14,7 @@
  * For more details, see http://www.mrtrix.org/.
  */
 
+#include <array>
 #include <fstream>
 #include <sstream>
 
@@ -254,7 +255,7 @@ void write(const Header &header, nlohmann::json &json, const std::string &image_
   }
 
   std::vector<size_t> order;
-  std::vector<bool> flip;
+  std::array<bool, 3> flip;
   File::NIfTI::axes_on_write(header, order, flip);
   if (order[0] == 0 && order[1] == 1 && order[2] == 2 && !flip[0] && !flip[1] && !flip[2]) {
     INFO(
diff --git a/core/file/nifti_utils.cpp b/core/file/nifti_utils.cpp
index 4d424d74a9..45ac9189a7 100644
--- a/core/file/nifti_utils.cpp
+++ b/core/file/nifti_utils.cpp
@@ -544,7 +544,7 @@ template <class NiftiHeader> void store(NiftiHeader &NH, const Header &H, const
   }
 }
 
-void axes_on_write(const Header &H, std::vector<size_t> &order, std::vector<bool> &flip) {
+void axes_on_write(const Header &H, std::vector<size_t> &order, std::array<bool, 3> &flip) {
   Stride::List strides = Stride::get(H);
   strides.resize(3);
   order = Stride::order(strides);
@@ -552,7 +552,7 @@ void axes_on_write(const Header &H, std::vector<size_t> &order, std::vector<bool
 }
 
 transform_type adjust_transform(const Header &H, std::vector<size_t> &axes) {
-  std::vector<bool> flip;
+  std::array<bool, 3> flip;
   axes_on_write(H, axes, flip);
 
   if (axes[0] == 0 && axes[1] == 1 && axes[2] == 2 && !flip[0] && !flip[1] && !flip[2])
diff --git a/core/file/nifti_utils.h b/core/file/nifti_utils.h
index a940bdcb8e..d5337edb92 100644
--- a/core/file/nifti_utils.h
+++ b/core/file/nifti_utils.h
@@ -17,6 +17,7 @@
 #ifndef __file_nifti_utils_h__
 #define __file_nifti_utils_h__
 
+#include <array>
 // nifti1_io.h and nifti2_io.h headers must be included after dirent.h (transitively included by header.h)
 // otherwise we run into definitions conflict on Linux
 // clang-format off
@@ -35,7 +36,7 @@ namespace File {
 namespace NIfTI {
 extern bool right_left_warning_issued;
 
-void axes_on_write(const Header &H, std::vector<size_t> &order, std::vector<bool> &flip);
+void axes_on_write(const Header &H, std::vector<size_t> &order, std::array<bool, 3> &flip);
 transform_type adjust_transform(const Header &H, std::vector<size_t> &order);
 
 bool check(int VERSION, Header &H, const size_t num_axes, const std::vector<std::string> &suffixes);
diff --git a/core/phase_encoding.h b/core/phase_encoding.h
index 0a2c6e8ad2..2921848aff 100644
--- a/core/phase_encoding.h
+++ b/core/phase_encoding.h
@@ -18,6 +18,7 @@
 #define __phaseencoding_h__
 
 #include <Eigen/Dense>
+#include <array>
 
 #include "app.h"
 #include "axes.h"
@@ -192,7 +193,7 @@ Eigen::MatrixXd transform_for_image_load(const MatrixType &pe_scheme, const Head
 template <class MatrixType, class HeaderType>
 Eigen::MatrixXd transform_for_nifti_write(const MatrixType &pe_scheme, const HeaderType &H) {
   std::vector<size_t> order;
-  std::vector<bool> flip;
+  std::array<bool, 3> flip;
   File::NIfTI::axes_on_write(H, order, flip);
   if (order[0] == 0 && order[1] == 1 && order[2] == 2 && !flip[0] && !flip[1] && !flip[2]) {
     INFO("No transformation of phase encoding data required for export to file");