diff --git a/CMakeLists.txt b/CMakeLists.txt
index e4e1d4d7..ff33bfbf 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -65,6 +65,8 @@ else()
       endif()
       set(COMPREHENSIVE_WARNING_FLAGS "-Wall -Wextra -Wpedantic -pedantic-errors -Werror -Wfatal-errors -Wno-psabi")
       set(CMAKE_CXX_FLAGS "${MORPH_HOST_DEFINITION} -g ${COMPREHENSIVE_WARNING_FLAGS} -march=native -O3")
+      # Make it possible to compile complex constexpr functions
+      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fconstexpr-ops-limit=5000000000")
     endif()
   else() # Windows
     # Set flags for Windows. /EHsc required for use of exceptions
@@ -175,9 +177,6 @@ if(wxWidgets_FOUND)
   endif()
 endif()
 
-# Make it possible to compile complex constexpr functions
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fconstexpr-ops-limit=5000000000")
-
 # rapidxml is bundled in the source, but its headers will be installed in ${CMAKE_INSTALL_PREFIX}/morph/, and they're symlinked in ${PROJECT_SOURCE_DIR}/morph
 #include_directories("${PROJECT_SOURCE_DIR}/include/rapidxml-1.13")
 
diff --git a/examples/CMakeLists.txt b/examples/CMakeLists.txt
index 7d194186..3ea4e1cd 100644
--- a/examples/CMakeLists.txt
+++ b/examples/CMakeLists.txt
@@ -155,10 +155,14 @@ if(ARMADILLO_FOUND)
     target_link_libraries(grid_image GLEW::GLEW)
   endif()
 
-  add_executable(grid_resampled_image grid_resampled_image.cpp)
-  target_link_libraries(grid_resampled_image OpenGL::GL glfw Freetype::Freetype)
-  if(USE_GLEW)
-    target_link_libraries(grid_resampled_image GLEW::GLEW)
+  # Like HexGrid::resampleImage, this one uses an omp call that only works on Mac with
+  # libomp, so avoid compiling this example on a Mac.
+  if(NOT APPLE)
+    add_executable(grid_resampled_image grid_resampled_image.cpp)
+    target_link_libraries(grid_resampled_image OpenGL::GL glfw Freetype::Freetype)
+    if(USE_GLEW)
+      target_link_libraries(grid_resampled_image GLEW::GLEW)
+    endif()
   endif()
 
   add_executable(grid_layout grid_layout.cpp)
@@ -215,16 +219,19 @@ if(USE_GLEW)
   target_link_libraries(scatter GLEW::GLEW)
 endif()
 
-add_executable(scatter_ico scatter_ico.cpp)
-target_link_libraries(scatter_ico OpenGL::GL glfw Freetype::Freetype)
-if(USE_GLEW)
-  target_link_libraries(scatter_ico GLEW::GLEW)
-endif()
+# This sphere example uses constexpr code
+if(NOT CMAKE_CXX_COMPILER_ID MATCHES Clang)
+  add_executable(scatter_ico scatter_ico.cpp)
+  target_link_libraries(scatter_ico OpenGL::GL glfw Freetype::Freetype)
+  if(USE_GLEW)
+    target_link_libraries(scatter_ico GLEW::GLEW)
+  endif()
 
-add_executable(scatter_geodesic scatter_geodesic.cpp)
-target_link_libraries(scatter_geodesic OpenGL::GL glfw Freetype::Freetype)
-if(USE_GLEW)
-  target_link_libraries(scatter_geodesic GLEW::GLEW)
+  add_executable(scatter_geodesic scatter_geodesic.cpp)
+  target_link_libraries(scatter_geodesic OpenGL::GL glfw Freetype::Freetype)
+  if(USE_GLEW)
+    target_link_libraries(scatter_geodesic GLEW::GLEW)
+  endif()
 endif()
 
 add_executable(scatter_hex_mercator scatter_hex_mercator.cpp)
@@ -341,10 +348,13 @@ if(USE_GLEW)
   target_link_libraries(rod GLEW::GLEW)
 endif()
 
-add_executable(grating grating.cpp)
-target_link_libraries(grating OpenGL::GL glfw Freetype::Freetype)
-if(USE_GLEW)
-  target_link_libraries(grating GLEW::GLEW)
+# This example uses constexpr code
+if(NOT CMAKE_CXX_COMPILER_ID MATCHES Clang)
+  add_executable(grating grating.cpp)
+  target_link_libraries(grating OpenGL::GL glfw Freetype::Freetype)
+  if(USE_GLEW)
+    target_link_libraries(grating GLEW::GLEW)
+  endif()
 endif()
 
 add_executable(cone cone.cpp)
@@ -353,36 +363,42 @@ if(USE_GLEW)
   target_link_libraries(cone GLEW::GLEW)
 endif()
 
-add_executable(sphere sphere.cpp)
-target_link_libraries(sphere OpenGL::GL glfw Freetype::Freetype)
-set_property(TARGET sphere PROPERTY CXX_STANDARD 20)
-if(USE_GLEW)
-  target_link_libraries(sphere GLEW::GLEW)
+# This sphere example uses constexpr code
+if(NOT CMAKE_CXX_COMPILER_ID MATCHES Clang)
+  add_executable(sphere sphere.cpp)
+  target_link_libraries(sphere OpenGL::GL glfw Freetype::Freetype)
+  set_property(TARGET sphere PROPERTY CXX_STANDARD 20)
+  if(USE_GLEW)
+    target_link_libraries(sphere GLEW::GLEW)
+  endif()
 endif()
 
-add_executable(icosahedron icosahedron.cpp)
-target_link_libraries(icosahedron OpenGL::GL glfw Freetype::Freetype)
-if(USE_GLEW)
-  target_link_libraries(icosahedron GLEW::GLEW)
-endif()
+# constexpr code won't work on Clang
+if(NOT CMAKE_CXX_COMPILER_ID MATCHES Clang)
+  add_executable(icosahedron icosahedron.cpp)
+  target_link_libraries(icosahedron OpenGL::GL glfw Freetype::Freetype)
+  if(USE_GLEW)
+    target_link_libraries(icosahedron GLEW::GLEW)
+  endif()
 
-# Need C++20 for the way I use constexpr here so that it is legal to
-# have "a definition of a variable for which no initialization is
-# performed".
-add_executable(testce testce.cpp)
-set_property(TARGET testce PROPERTY CXX_STANDARD 20)
+  # Need C++20 for the way I use constexpr here so that it is legal to
+  # have "a definition of a variable for which no initialization is
+  # performed".
+  add_executable(testce testce.cpp)
+  set_property(TARGET testce PROPERTY CXX_STANDARD 20)
 
-add_executable(geodesic geodesic.cpp)
-target_link_libraries(geodesic OpenGL::GL glfw Freetype::Freetype)
-if(USE_GLEW)
-  target_link_libraries(geodesic GLEW::GLEW)
-endif()
+  add_executable(geodesic geodesic.cpp)
+  target_link_libraries(geodesic OpenGL::GL glfw Freetype::Freetype)
+  if(USE_GLEW)
+    target_link_libraries(geodesic GLEW::GLEW)
+  endif()
 
-add_executable(geodesic_ce geodesic_ce.cpp)
-set_property(TARGET geodesic_ce PROPERTY CXX_STANDARD 20)
-target_link_libraries(geodesic_ce OpenGL::GL glfw Freetype::Freetype)
-if(USE_GLEW)
-  target_link_libraries(geodesic_ce GLEW::GLEW)
+  add_executable(geodesic_ce geodesic_ce.cpp)
+  set_property(TARGET geodesic_ce PROPERTY CXX_STANDARD 20)
+  target_link_libraries(geodesic_ce OpenGL::GL glfw Freetype::Freetype)
+  if(USE_GLEW)
+    target_link_libraries(geodesic_ce GLEW::GLEW)
+  endif()
 endif()
 
 add_executable(tri tri.cpp)
diff --git a/examples/helloworld.cpp b/examples/helloworld.cpp
index c79f92a6..93b81935 100644
--- a/examples/helloworld.cpp
+++ b/examples/helloworld.cpp
@@ -1,7 +1,7 @@
 #include <morph/Visual.h>
 int main()
 {
-    morph::Visual<morph::gl::version_3_1_es> v(600, 400, "Hello World!");
+    morph::Visual<morph::gl::version_4_1> v(600, 400, "Hello World!");
     v.addLabel ("Hello World!", {0,0,0});
     v.keepOpen();
     return 0;
diff --git a/morph/AllocAndRead.h b/morph/AllocAndRead.h
index 78b8176d..3699f541 100644
--- a/morph/AllocAndRead.h
+++ b/morph/AllocAndRead.h
@@ -11,7 +11,7 @@
 #include <string>
 #include <sstream>
 #include <fstream>
-#include <cuchar>
+#include <cstddef>
 #include <stdexcept>
 #include <stdlib.h>
 #include <string.h>
diff --git a/morph/BezCurve.h b/morph/BezCurve.h
index 954be072..f0530289 100644
--- a/morph/BezCurve.h
+++ b/morph/BezCurve.h
@@ -15,7 +15,7 @@
 #include <sstream>
 #include <stdexcept>
 #include <cmath>
-#include <cuchar>
+#include <cstddef>
 #ifdef __ICC__
 # define ARMA_ALLOW_FAKE_GCC 1
 #endif
diff --git a/morph/ColourMap_Lists.h b/morph/ColourMap_Lists.h
index 3b3c671b..f80b93d2 100644
--- a/morph/ColourMap_Lists.h
+++ b/morph/ColourMap_Lists.h
@@ -1,6 +1,6 @@
 #pragma once
 
-#include <cuchar>
+#include <cstddef>
 
 /*!
  * Listed colour maps, copied from _cm_listed.py
diff --git a/morph/HdfData.h b/morph/HdfData.h
index ffe6a1d8..680c9cd6 100644
--- a/morph/HdfData.h
+++ b/morph/HdfData.h
@@ -18,7 +18,7 @@
 #include <string>
 #include <utility>
 #include <bitset>
-#include <cuchar>
+#include <cstddef>
 #include <sstream>
 #include <stdexcept>
 #include <morph/vec.h>
diff --git a/morph/MathAlgo.h b/morph/MathAlgo.h
index 893056fa..5176f974 100644
--- a/morph/MathAlgo.h
+++ b/morph/MathAlgo.h
@@ -10,7 +10,7 @@
 #include <algorithm>
 #include <bitset>
 #include <memory>
-#include <cuchar>
+#include <cstddef>
 #include <morph/vec.h>
 #include <morph/vvec.h>
 #include <morph/range.h>
diff --git a/morph/PointRowsVisual.h b/morph/PointRowsVisual.h
index 40abf699..944f3ede 100644
--- a/morph/PointRowsVisual.h
+++ b/morph/PointRowsVisual.h
@@ -8,7 +8,7 @@
 #include <iostream>
 #include <vector>
 #include <array>
-#include <cuchar>
+#include <cstddef>
 
 namespace morph {
 
diff --git a/morph/Random.h b/morph/Random.h
index a08ac1bf..dfc8b2cb 100644
--- a/morph/Random.h
+++ b/morph/Random.h
@@ -7,7 +7,7 @@
 #include <string>
 #include <ostream>
 #include <array>
-#include <cuchar>
+#include <cstddef>
 #include <memory>
 
 /*!
diff --git a/morph/Scale.h b/morph/Scale.h
index 28fd3c90..859c2eeb 100644
--- a/morph/Scale.h
+++ b/morph/Scale.h
@@ -40,7 +40,7 @@
 
 #include <stdexcept>
 #include <cmath>
-#include <cuchar>
+#include <cstddef>
 #include <string>
 #include <sstream>
 #include <morph/MathAlgo.h>
@@ -77,7 +77,7 @@ namespace morph {
      * integers.
      */
     template <typename T, typename S>
-    class ScaleImplBase
+    struct ScaleImplBase
     {
     public:
         /*!
diff --git a/morph/Visual.h b/morph/Visual.h
index 014d1c7d..a9caf6bb 100644
--- a/morph/Visual.h
+++ b/morph/Visual.h
@@ -78,7 +78,7 @@
 #include <memory>
 #include <functional>
 #include <chrono>
-#include <cuchar>
+#include <cstddef>
 
 #include <morph/VisualDefaultShaders.h>
 
diff --git a/morph/VisualModel.h b/morph/VisualModel.h
index 00983e7e..21c7cb32 100644
--- a/morph/VisualModel.h
+++ b/morph/VisualModel.h
@@ -44,7 +44,7 @@
 #include <string>
 #include <memory>
 #include <functional>
-#include <cuchar>
+#include <cstddef>
 
 // Switches on some changes where I carefully unbind gl buffers after calling
 // glBufferData() and rebind when changing the vertex model. Makes no difference on my
diff --git a/morph/bn/Basins.h b/morph/bn/Basins.h
index d1fe0ab5..0feb55da 100644
--- a/morph/bn/Basins.h
+++ b/morph/bn/Basins.h
@@ -12,7 +12,7 @@
 #include <map>
 #include <set>
 #include <vector>
-#include <cuchar>
+#include <cstddef>
 
 namespace morph {
     namespace bn {
diff --git a/morph/bn/GeneNet.h b/morph/bn/GeneNet.h
index 6a6d14aa..b3369903 100644
--- a/morph/bn/GeneNet.h
+++ b/morph/bn/GeneNet.h
@@ -15,7 +15,7 @@
 #include <vector>
 #include <bitset>
 #include <list>
-#include <cuchar>
+#include <cstddef>
 #include <math.h>
 #include <immintrin.h> // Using intrinsics for computing Hamming distances
 #include <morph/bn/Genome.h>
diff --git a/morph/bn/GeneNetDual.h b/morph/bn/GeneNetDual.h
index e7b65ff7..9eebc57a 100644
--- a/morph/bn/GeneNetDual.h
+++ b/morph/bn/GeneNetDual.h
@@ -4,7 +4,7 @@
 #include <morph/bn/Genome.h>
 #include <morph/bn/GeneNet.h>
 #include <set>
-#include <cuchar>
+#include <cstddef>
 
 namespace morph {
     namespace  bn {
diff --git a/morph/bn/Genome.h b/morph/bn/Genome.h
index 423a1fcc..39430f77 100644
--- a/morph/bn/Genome.h
+++ b/morph/bn/Genome.h
@@ -12,7 +12,7 @@
 #include <bitset>
 #include <iostream>
 #include <sstream>
-#include <cuchar>
+#include <cstddef>
 #include <immintrin.h>
 #include <morph/tools.h>
 #include <morph/bn/Random.h>
diff --git a/morph/bn/Genosect.h b/morph/bn/Genosect.h
index 51f660a1..e514e29a 100644
--- a/morph/bn/Genosect.h
+++ b/morph/bn/Genosect.h
@@ -1,6 +1,6 @@
 #pragma once
 
-#include <cuchar>
+#include <cstddef>
 
 namespace morph {
     namespace  bn {
diff --git a/morph/bn/GradGenome.h b/morph/bn/GradGenome.h
index dd8f5f4c..1968ea88 100644
--- a/morph/bn/GradGenome.h
+++ b/morph/bn/GradGenome.h
@@ -13,7 +13,7 @@
 #include <bitset>
 #include <iostream>
 #include <sstream>
-#include <cuchar>
+#include <cstddef>
 #include <immintrin.h>
 #include <morph/tools.h>
 #include <morph/bn/Random.h>
diff --git a/morph/bn/GradGenosect.h b/morph/bn/GradGenosect.h
index 0786bb59..c247d87f 100644
--- a/morph/bn/GradGenosect.h
+++ b/morph/bn/GradGenosect.h
@@ -1,6 +1,6 @@
 #pragma once
 
-#include <cuchar>
+#include <cstddef>
 
 namespace morph {
     namespace  bn {
diff --git a/morph/bn/Quine.h b/morph/bn/Quine.h
index e91a8d54..c3c9a6b0 100644
--- a/morph/bn/Quine.h
+++ b/morph/bn/Quine.h
@@ -5,7 +5,7 @@
 #include <sstream>
 #include <string>
 #include <vector>
-#include <cuchar>
+#include <cstddef>
 #include <algorithm>
 #include <morph/bn/Implicant.h>
 
diff --git a/morph/bn/Random.h b/morph/bn/Random.h
index fb5534c6..b47bbcc6 100644
--- a/morph/bn/Random.h
+++ b/morph/bn/Random.h
@@ -5,7 +5,7 @@
 #pragma once
 
 #include <array>
-#include <cuchar>
+#include <cstddef>
 #include <morph/Random.h>
 #include <morph/bn/Genosect.h>
 
diff --git a/morph/gl/compute_shaderprog.h b/morph/gl/compute_shaderprog.h
index c4e22695..806a8ca5 100644
--- a/morph/gl/compute_shaderprog.h
+++ b/morph/gl/compute_shaderprog.h
@@ -3,7 +3,7 @@
 #include <vector>
 #include <string>
 #include <sstream>
-#include <cuchar>
+#include <cstddef>
 #include <morph/gl/version.h>
 #include <morph/gl/util.h>
 #include <morph/vec.h>
diff --git a/morph/gl/shaders.h b/morph/gl/shaders.h
index c65dc199..0536c7f9 100644
--- a/morph/gl/shaders.h
+++ b/morph/gl/shaders.h
@@ -130,12 +130,12 @@ namespace morph {
                 if (morph::Tools::fileExists (entry.filename)) {
                     std::cout << "Using " << morph::gl::shader_type_str(entry.type)
                               << " shader from the file " << entry.filename << std::endl;
-                    source = std::move (morph::gl::ReadShader (entry.filename));
+                    source = morph::gl::ReadShader (entry.filename);
                 } else {
                     if constexpr (debug_shaders == true) {
                         std::cout << "Using compiled-in " << morph::gl::shader_type_str(entry.type) << " shader\n";
                     }
-                    source = std::move (morph::gl::ReadDefaultShader (entry.compiledIn));
+                    source = morph::gl::ReadDefaultShader (entry.compiledIn);
                 }
                 if (source == nullptr) {
                     for (auto entry : shader_info) {
diff --git a/morph/gl/ssbo.h b/morph/gl/ssbo.h
index 56e12149..f2aabf8d 100644
--- a/morph/gl/ssbo.h
+++ b/morph/gl/ssbo.h
@@ -9,7 +9,7 @@
  * Author: Seb James.
  */
 
-#include <cuchar>
+#include <cstddef>
 #include <morph/vec.h>
 #include <morph/vvec.h>
 #include <morph/range.h>
diff --git a/morph/loadpng.h b/morph/loadpng.h
index c2dbe614..71f709b3 100644
--- a/morph/loadpng.h
+++ b/morph/loadpng.h
@@ -11,7 +11,7 @@
 #include <type_traits>
 #include <vector>
 #include <string>
-#include <cuchar>
+#include <cstddef>
 #include <stdexcept>
 #include <morph/vec.h>
 #include <morph/vvec.h>
diff --git a/morph/vec.h b/morph/vec.h
index cd651022..2e5f5c90 100644
--- a/morph/vec.h
+++ b/morph/vec.h
@@ -19,7 +19,7 @@
 #include <iomanip>
 #include <algorithm>
 #include <functional>
-#include <cuchar>
+#include <cstddef>
 #include <morph/Random.h>
 #include <morph/range.h>
 
diff --git a/morph/vvec.h b/morph/vvec.h
index c81ce4b7..7dd59853 100644
--- a/morph/vvec.h
+++ b/morph/vvec.h
@@ -19,7 +19,7 @@
 #include <iomanip>
 #include <algorithm>
 #include <functional>
-#include <cuchar>
+#include <cstddef>
 #include <morph/Random.h>
 #include <morph/range.h>
 #include <morph/trait_tests.h>
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 7400c8b0..efd3c623 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -249,21 +249,27 @@ add_test(testConfig testConfig)
 add_executable(testQuaternion testQuaternion.cpp)
 add_test(testQuaternion testQuaternion)
 
-add_executable(testQuat_constexpr testQuat_constexpr.cpp)
-set_property(TARGET testQuat_constexpr PROPERTY CXX_STANDARD 20)
-add_test(testQuat_constexpr testQuat_constexpr)
+# Note that we only compile the constexpr tests if compiler is not Clang. Clang doesn't like std::abs,
+# std::sin (etc) within a constexpr function.
+if(NOT CMAKE_CXX_COMPILER_ID MATCHES Clang)
+  add_executable(testQuat_constexpr testQuat_constexpr.cpp)
+  set_property(TARGET testQuat_constexpr PROPERTY CXX_STANDARD 20)
+  add_test(testQuat_constexpr testQuat_constexpr)
+endif()
 
 # test morph::vec.
 add_executable(testvec testvec.cpp)
 add_test(testvec testvec)
 
-# constexpr functionality in morph::vec
-# Need C++20 for the way I use constexpr here so that it is legal to
-# have "a definition of a variable for which no initialization is
-# performed".
-add_executable(testvec_constexpr testvec_constexpr.cpp)
-set_property(TARGET testvec_constexpr PROPERTY CXX_STANDARD 20)
-add_test(testvec_constexpr testvec_constexpr)
+if(NOT CMAKE_CXX_COMPILER_ID MATCHES Clang)
+  # constexpr functionality in morph::vec
+  # Need C++20 for the way I use constexpr here so that it is legal to
+  # have "a definition of a variable for which no initialization is
+  # performed".
+  add_executable(testvec_constexpr testvec_constexpr.cpp)
+  set_property(TARGET testvec_constexpr PROPERTY CXX_STANDARD 20)
+  add_test(testvec_constexpr testvec_constexpr)
+endif()
 
 add_executable(testvec_asmapkey testvec_asmapkey.cpp)
 add_test(testvec_asmapkey testvec_asmapkey)
@@ -328,10 +334,12 @@ add_test(testScaleVector testScaleVector)
 add_executable(testTransformMatrix testTransformMatrix.cpp)
 add_test(testTransformMatrix testTransformMatrix)
 
-# constexpr TransformMatrix
-add_executable(testTransMat_constexpr testTransMat_constexpr.cpp)
-set_property(TARGET testTransMat_constexpr PROPERTY CXX_STANDARD 20)
-add_test(testTransMat_constexpr testTransMat_constexpr)
+if(NOT CMAKE_CXX_COMPILER_ID MATCHES Clang)
+  # constexpr TransformMatrix
+  add_executable(testTransMat_constexpr testTransMat_constexpr.cpp)
+  set_property(TARGET testTransMat_constexpr PROPERTY CXX_STANDARD 20)
+  add_test(testTransMat_constexpr testTransMat_constexpr)
+endif()
 
 # Test morph::Matrix33 (3x3 matrix)
 add_executable(testMatrix33 testMatrix33.cpp)