diff --git a/tests/testthat.R b/tests/testthat.R
index 7be6139..ccda5a5 100644
--- a/tests/testthat.R
+++ b/tests/testthat.R
@@ -1,4 +1,14 @@
 library(testthat)
 library(freesurferformats)
 
+#' @title Determine whether a test is running on CRAN under macos
+#'
+#' @description We are currently getting failed unit tests on CRAN under macos, while the package works under MacOS on both <https://builder.r-hub.io/> and on our MacOS machines. This is because the package file cache does not work on CRAN, as the HOME is mounted read-only on the CRAN test systems. So we have to skip the tests that require optional data under MacOS on CRAN.
+#'
+#' @return logical, whether a test is running on CRAN under MacOS
+#' @keywords internal
+tests_running_on_cran_under_macos <- function() {
+  return(tolower(Sys.info()[["sysname"]]) == 'darwin' && !identical(Sys.getenv("NOT_CRAN"), "true"));
+}
+
 test_check("freesurferformats")
diff --git a/tests/testthat/test-read-fs-surface.R b/tests/testthat/test-read-fs-surface.R
index 3cbb241..41e0842 100644
--- a/tests/testthat/test-read-fs-surface.R
+++ b/tests/testthat/test-read-fs-surface.R
@@ -1,5 +1,10 @@
+
+
+
+
 test_that("Our demo surface file can be read using read.fs.surface", {
 
+  skip_if(tests_running_on_cran_under_macos(), message = "Skipping on CRAN under MacOS, required test data cannot be downloaded.");
   freesurferformats::download_optional_data();
   subjects_dir = freesurferformats::get_optional_data_filepath("subjects_dir");
   surface_file = file.path(subjects_dir, "subject1", "surf", "lh.white");
@@ -29,6 +34,9 @@ test_that("Our demo surface file can be read using read.fs.surface", {
 test_that("Vertex connectivity in the demo surface file is as expected from reference implementation", {
   # Checks for bug in issue #8: freesurfer surface import - row-major/column-major order
   # The vertex connectivities used in this test are known from running the FreeSurfer Matlab function $FREESURFER_HOME/matlab/read_surf.m on the data
+
+  skip_if(tests_running_on_cran_under_macos(), message = "Skipping on CRAN under MacOS, required test data cannot be downloaded.");
+
   freesurferformats::download_optional_data();
   subjects_dir = freesurferformats::get_optional_data_filepath("subjects_dir");
   surface_file = file.path(subjects_dir, "subject1", "surf", "lh.white");
@@ -49,6 +57,8 @@ test_that("Vertex connectivity in the demo surface file is as expected from refe
 test_that("The vertices of a face are close to each other", {
   # Checks for bug in issue #8: freesurfer surface import - row-major/column-major order
 
+  skip_if(tests_running_on_cran_under_macos(), message = "Skipping on CRAN under MacOS, required test data cannot be downloaded.");
+
   freesurferformats::download_optional_data();
   subjects_dir = freesurferformats::get_optional_data_filepath("subjects_dir");
   surface_file = file.path(subjects_dir, "subject1", "surf", "lh.white");
diff --git a/tests/testthat/test-write-fs-surface.R b/tests/testthat/test-write-fs-surface.R
index d9b3407..ba6201d 100644
--- a/tests/testthat/test-write-fs-surface.R
+++ b/tests/testthat/test-write-fs-surface.R
@@ -35,6 +35,9 @@ test_that("One can write and re-read triangular surface data", {
 })
 
 test_that("One can read, write and re-read triangular surface data", {
+
+  skip_if(tests_running_on_cran_under_macos(), message = "Skipping on CRAN under MacOS, required test data cannot be downloaded.");
+
   freesurferformats::download_optional_data();
   subjects_dir = freesurferformats::get_optional_data_filepath("subjects_dir");
   surface_file = file.path(subjects_dir, "subject1", "surf", "lh.white");