diff --git a/CMakeLists.txt b/CMakeLists.txt
index 46527cbca0..dd24534c94 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -112,7 +112,7 @@ else ()
 endif ()
 option (${PROJ_NAME}_BUILD_TOOLS "Build the command-line tools" ON)
 option (${PROJ_NAME}_BUILD_TESTS "Build the unit tests" ON)
-set_option (OIIO_USE_HWY "Enable experimental Google Highway SIMD optimizations (if Highway is available)" OFF)
+set_option (OIIO_USE_HWY "Enable experimental Google Highway SIMD optimizations (if Highway is available)" OFF VERBOSE)
 set (OIIO_LIBNAME_SUFFIX "" CACHE STRING
      "Optional name appended to ${PROJECT_NAME} libraries that are built")
 option (BUILD_OIIOUTIL_ONLY "If ON, will build *only* libOpenImageIO_Util" OFF)
diff --git a/src/cmake/testing.cmake b/src/cmake/testing.cmake
index a954a83d21..a209c50524 100644
--- a/src/cmake/testing.cmake
+++ b/src/cmake/testing.cmake
@@ -30,6 +30,7 @@ set(OIIO_TESTSUITE_IMAGEDIR "${PROJECT_BINARY_DIR}/testsuite" CACHE PATH
 #                    [ URL http://find.reference.cases.here.com ]
 #                    [ FOUNDVAR variable_name ... ]
 #                    [ ENABLEVAR variable_name ... ]
+#                    [ DISABLEVAR variable_name ... ]
 #                    [ SUFFIX suffix ]
 #                    [ ENVIRONMENT "VAR=value" ... ]
 #                  )
@@ -43,7 +44,11 @@ set(OIIO_TESTSUITE_IMAGEDIR "${PROJECT_BINARY_DIR}/testsuite" CACHE PATH
 # not existing and true, will skip the test.
 #
 # The optional ENABLEVAR introduces variables (typically ENABLE_Foo) that
-# if existing and yet false, will skip the test.
+# if existing and yet false/off/zero, will skip the test. (Not existing
+# does NOT disable the test.)
+#
+# The optional DISABLEVAR introduces variables that, if existing and
+# true/on/nonzero, will skip the test.
 #
 # The optional SUFFIX is appended to the test name.
 #
@@ -51,7 +56,7 @@ set(OIIO_TESTSUITE_IMAGEDIR "${PROJECT_BINARY_DIR}/testsuite" CACHE PATH
 # test.
 #
 macro (oiio_add_tests)
-    cmake_parse_arguments (_ats "" "SUFFIX;TESTNAME" "URL;IMAGEDIR;LABEL;FOUNDVAR;ENABLEVAR;ENVIRONMENT" ${ARGN})
+    cmake_parse_arguments (_ats "" "SUFFIX;TESTNAME" "URL;IMAGEDIR;LABEL;FOUNDVAR;ENABLEVAR;DISABLEVAR;ENVIRONMENT" ${ARGN})
        # Arguments: <prefix> <options> <one_value_keywords> <multi_value_keywords> args...
     set (_ats_testdir "${OIIO_TESTSUITE_IMAGEDIR}/${_ats_IMAGEDIR}")
     # If there was a FOUNDVAR param specified and that variable name is
@@ -59,6 +64,7 @@ macro (oiio_add_tests)
     set (_test_disabled FALSE)
     set (_test_notfound FALSE)
     foreach (_var ${_ats_FOUNDVAR})
+        # FOUNDVAR entires had better exist and be true
         if (NOT ${_var})
             set (_ats_LABEL "broken")
             set (_test_notfound TRUE)
@@ -66,12 +72,20 @@ macro (oiio_add_tests)
     endforeach ()
     set (_test_disabled 0)
     foreach (_var ${_ats_ENABLEVAR})
+        # ENABLEVAR, *if* it exists, must be true. But not existing is fine.
         if ((NOT "${${_var}}" STREQUAL "" AND NOT "${${_var}}") OR
             (NOT "$ENV{${_var}}" STREQUAL "" AND NOT "$ENV{${_var}}"))
             set (_ats_LABEL "broken")
             set (_test_disabled TRUE)
         endif ()
     endforeach ()
+    foreach (_var ${_ats_DISABLEVAR})
+        # DISABLEVAR, if true, disable the test. Not existing is fine.
+        if (${_var})
+            set (_ats_LABEL "broken")
+            set (_test_disabled TRUE)
+        endif ()
+    endforeach ()
     # For OCIO 2.2+, have the testsuite use the default built-in config
     list (APPEND _ats_ENVIRONMENT "OCIO=ocio://default"
                                   "OIIO_TESTSUITE_OCIOCONFIG=ocio://default")
@@ -238,6 +252,27 @@ macro (oiio_add_all_tests)
     oiio_add_tests (oiiotool-color
                     FOUNDVAR OpenColorIO_FOUND)
 
+    # Tests to run with HWY enabled.
+    # Remember to add tests here as hwy enabled IBA functions are added
+    oiio_add_tests ( oiiotool
+                     oiiotool-composite
+                     oiiotool-xform
+                     docs-examples-cpp
+        FOUNDVAR hwy_FOUND
+        ENABLEVAR OIIO_USE_HWY
+        SUFFIX ".hwy"
+        ENVIRONMENT "OPENIMAGEIO_ENABLE_HWY=1"
+        )
+
+    oiio_add_tests ( python-imagebufalgo
+        FOUNDVAR hwy_FOUND
+        ENABLEVAR OIIO_USE_HWY  USE_PYTHON
+        DISABLEVAR BUILD_OIIOUTIL_ONLY SANITIZE
+        SUFFIX ".hwy"
+        ENVIRONMENT "OPENIMAGEIO_ENABLE_HWY=1"
+        IMAGEDIR oiio-images
+        )
+
     # List testsuites for specific formats or features which might be not found
     # or be intentionally disabled, or which need special external reference
     # images from the web that if not found, should skip the tests:
diff --git a/src/libOpenImageIO/CMakeLists.txt b/src/libOpenImageIO/CMakeLists.txt
index 262c85f4dd..04fcf58f2f 100644
--- a/src/libOpenImageIO/CMakeLists.txt
+++ b/src/libOpenImageIO/CMakeLists.txt
@@ -282,6 +282,7 @@ if (OIIO_BUILD_TESTS AND BUILD_TESTING)
                                          ${OpenCV_LIBRARIES}
                                          ${OPENIMAGEIO_IMATH_TARGETS}
                           FOLDER "Unit Tests" NO_INSTALL)
+    target_compile_definitions (imagebufalgo_test PRIVATE OIIO_USE_HWY=${_oiio_use_hwy})
     add_test (unit_imagebufalgo ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}/imagebufalgo_test)
 
     fancy_add_executable (NAME imagespec_test SRC imagespec_test.cpp
diff --git a/src/libOpenImageIO/imagebufalgo_test.cpp b/src/libOpenImageIO/imagebufalgo_test.cpp
index cf9c0de7bf..763ece2577 100644
--- a/src/libOpenImageIO/imagebufalgo_test.cpp
+++ b/src/libOpenImageIO/imagebufalgo_test.cpp
@@ -43,6 +43,10 @@ static bool wedge         = false;
 static int threadcounts[] = { 1,  2,  4,  8,  12,  16,   20,
                               24, 28, 32, 64, 128, 1024, 1 << 30 };
 
+static const int hwy_build = OIIO_USE_HWY;
+static int hwy_on          = hwy_build;
+
+
 
 static void
 getargs(int argc, char* argv[])
@@ -403,7 +407,7 @@ test_channel_append()
 void
 test_add()
 {
-    std::cout << "test add\n";
+    print("test add{}\n", hwy_on ? " (HWY)" : "");
 
     // Create buffers
     const float Aval[] = { 0.1f, 0.2f, 0.3f, 0.4f };
@@ -429,7 +433,7 @@ test_add()
 void
 test_sub()
 {
-    std::cout << "test sub\n";
+    print("test sub{}\n", hwy_on ? " (HWY)" : "");
 
     // Create buffers
     const float Aval[] = { 0.1f, 0.2f, 0.3f, 0.4f };
@@ -455,7 +459,7 @@ test_sub()
 void
 test_mul()
 {
-    std::cout << "test mul\n";
+    print("test mul{}\n", hwy_on ? " (HWY)" : "");
 
     // Create buffers
     // Create buffers
@@ -482,7 +486,7 @@ test_mul()
 void
 test_mad()
 {
-    std::cout << "test mad\n";
+    print("test mad{}\n", hwy_on ? " (HWY)" : "");
     const int WIDTH = 4, HEIGHT = 4, CHANNELS = 4;
     ImageSpec spec(WIDTH, HEIGHT, CHANNELS, TypeDesc::FLOAT);
 
@@ -1678,6 +1682,17 @@ test_demosaic()
 }
 
 
+
+// clang-format off
+// Neat trick macro to prefix in front of the calls where we want to
+// run it in both hwy and non-hwy modes. It will loop over both settings.
+#define HWY_TEST                                    \
+    for (hwy_on = 0; hwy_on <= hwy_build; ++hwy_on) \
+        OIIO::attribute("enable_hwy", hwy_on), /* next command */
+// clang-format on
+
+
+
 int
 main(int argc, char** argv)
 {
@@ -1702,10 +1717,10 @@ main(int argc, char** argv)
     test_crop();
     test_paste();
     test_channel_append();
-    test_add();
-    test_sub();
-    test_mul();
-    test_mad();
+    HWY_TEST test_add();
+    HWY_TEST test_sub();
+    HWY_TEST test_mul();
+    HWY_TEST test_mad();
     test_hwy_strided_roi_fallback();
     test_min();
     test_max();