diff --git a/CHANGES b/CHANGES
index 52b99bc..c2d2f59 100644
--- a/CHANGES
+++ b/CHANGES
@@ -14,6 +14,7 @@ Version 0.1.11
 - add support for writing GIFTI format annotations
 - export rotate2D and flip2D to namespace
 - add support for reading transformation matrices from xfm files: read.fs.transform
+- rename all optional data functions: replace optional_data with opt_data in function names to prevent clash with fsbrain names
 
 
 Version 0.1.10
diff --git a/NAMESPACE b/NAMESPACE
index 9fe479d..7561927 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -11,15 +11,15 @@ S3method(read_nisurfacefile,fsnative)
 S3method(read_nisurfacefile,gifti)
 export(cdata)
 export(colortable.from.annot)
-export(delete_all_optional_data)
-export(download_optional_data)
+export(delete_all_opt_data)
+export(download_opt_data)
 export(faces.quad.to.tris)
 export(flip2D)
 export(flip3D)
 export(fs.get.morph.file.ext.for.format)
 export(fs.get.morph.file.format.from.filename)
 export(fs.patch)
-export(get_optional_data_filepath)
+export(get_opt_data_filepath)
 export(gifti_writer)
 export(gifti_xml)
 export(gifti_xml_add_global_metadata)
@@ -29,7 +29,7 @@ export(is.fs.annot)
 export(is.fs.label)
 export(is.fs.surface)
 export(is.fs.volume)
-export(list_optional_data)
+export(list_opt_data)
 export(mghheader.centervoxelRAS.from.firstvoxelRAS)
 export(mghheader.crs.orientation)
 export(mghheader.is.conformed)
diff --git a/R/optdata.R b/R/optdata.R
index ebeae8e..5b91a35 100644
--- a/R/optdata.R
+++ b/R/optdata.R
@@ -6,7 +6,7 @@
 #'
 #' @export
 #' @importFrom pkgfilecache get_pkg_info ensure_files_available
-download_optional_data <- function() {
+download_opt_data <- function() {
   pkg_info = pkgfilecache::get_pkg_info("freesurferformats");
 
   # Replace these with your optional data files.
@@ -94,7 +94,7 @@ download_optional_data <- function() {
 #'
 #' @export
 #' @importFrom pkgfilecache get_pkg_info list_available
-list_optional_data <- function() {
+list_opt_data <- function() {
   pkg_info = pkgfilecache::get_pkg_info("freesurferformats");
   return(pkgfilecache::list_available(pkg_info));
 }
@@ -110,7 +110,7 @@ list_optional_data <- function() {
 #'
 #' @export
 #' @importFrom pkgfilecache get_pkg_info get_filepath
-get_optional_data_filepath <- function(filename, mustWork=TRUE) {
+get_opt_data_filepath <- function(filename, mustWork=TRUE) {
   pkg_info = pkgfilecache::get_pkg_info("freesurferformats");
   return(pkgfilecache::get_filepath(pkg_info, filename, mustWork=mustWork));
 }
@@ -122,7 +122,7 @@ get_optional_data_filepath <- function(filename, mustWork=TRUE) {
 #'
 #' @export
 #' @importFrom pkgfilecache get_pkg_info erase_file_cache
-delete_all_optional_data <- function() {
+delete_all_opt_data <- function() {
   pkg_info = pkgfilecache::get_pkg_info("freesurferformats");
   return(pkgfilecache::erase_file_cache(pkg_info));
 }
diff --git a/man/delete_all_optional_data.Rd b/man/delete_all_opt_data.Rd
similarity index 78%
rename from man/delete_all_optional_data.Rd
rename to man/delete_all_opt_data.Rd
index c5dda60..8f635cb 100644
--- a/man/delete_all_optional_data.Rd
+++ b/man/delete_all_opt_data.Rd
@@ -1,10 +1,10 @@
 % Generated by roxygen2: do not edit by hand
 % Please edit documentation in R/optdata.R
-\name{delete_all_optional_data}
-\alias{delete_all_optional_data}
+\name{delete_all_opt_data}
+\alias{delete_all_opt_data}
 \title{Delete all data in the package cache.}
 \usage{
-delete_all_optional_data()
+delete_all_opt_data()
 }
 \value{
 integer. The return value of the unlink() call: 0 for success, 1 for failure. See the unlink() documentation for details.
diff --git a/man/download_optional_data.Rd b/man/download_opt_data.Rd
similarity index 90%
rename from man/download_optional_data.Rd
rename to man/download_opt_data.Rd
index f88b809..96f3735 100644
--- a/man/download_optional_data.Rd
+++ b/man/download_opt_data.Rd
@@ -1,10 +1,10 @@
 % Generated by roxygen2: do not edit by hand
 % Please edit documentation in R/optdata.R
-\name{download_optional_data}
-\alias{download_optional_data}
+\name{download_opt_data}
+\alias{download_opt_data}
 \title{Download optional data for the freesurferformats package.}
 \usage{
-download_optional_data()
+download_opt_data()
 }
 \value{
 Named list. The list has entries: "available": vector of strings. The names of the files that are available in the local file cache. You can access them using get_optional_data_file(). "missing": vector of strings. The names of the files that this function was unable to retrieve.
diff --git a/man/get_optional_data_filepath.Rd b/man/get_opt_data_filepath.Rd
similarity index 84%
rename from man/get_optional_data_filepath.Rd
rename to man/get_opt_data_filepath.Rd
index 8a01583..dc36941 100644
--- a/man/get_optional_data_filepath.Rd
+++ b/man/get_opt_data_filepath.Rd
@@ -1,10 +1,10 @@
 % Generated by roxygen2: do not edit by hand
 % Please edit documentation in R/optdata.R
-\name{get_optional_data_filepath}
-\alias{get_optional_data_filepath}
+\name{get_opt_data_filepath}
+\alias{get_opt_data_filepath}
 \title{Access a single file from the package cache by its file name.}
 \usage{
-get_optional_data_filepath(filename, mustWork = TRUE)
+get_opt_data_filepath(filename, mustWork = TRUE)
 }
 \arguments{
 \item{filename, }{string. The filename of the file in the package cache.}
diff --git a/man/list_optional_data.Rd b/man/list_opt_data.Rd
similarity index 84%
rename from man/list_optional_data.Rd
rename to man/list_opt_data.Rd
index edd6578..fa15267 100644
--- a/man/list_optional_data.Rd
+++ b/man/list_opt_data.Rd
@@ -1,10 +1,10 @@
 % Generated by roxygen2: do not edit by hand
 % Please edit documentation in R/optdata.R
-\name{list_optional_data}
-\alias{list_optional_data}
+\name{list_opt_data}
+\alias{list_opt_data}
 \title{Get file names available in package cache.}
 \usage{
-list_optional_data()
+list_opt_data()
 }
 \value{
 vector of strings. The file names available, relative to the package cache.
diff --git a/tests/testthat/test-read-fs-surface.R b/tests/testthat/test-read-fs-surface.R
index 2aaf5fe..568b5d4 100644
--- a/tests/testthat/test-read-fs-surface.R
+++ b/tests/testthat/test-read-fs-surface.R
@@ -3,8 +3,8 @@
 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");
+  freesurferformats::download_opt_data();
+  subjects_dir = freesurferformats::get_opt_data_filepath("subjects_dir");
   surface_file = file.path(subjects_dir, "subject1", "surf", "lh.white");
   skip_if_not(file.exists(surface_file), message="Test data missing.") ;
 
@@ -36,8 +36,8 @@ test_that("Vertex connectivity in the demo surface file is as expected from refe
 
   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");
+  freesurferformats::download_opt_data();
+  subjects_dir = freesurferformats::get_opt_data_filepath("subjects_dir");
   surface_file = file.path(subjects_dir, "subject1", "surf", "lh.white");
   skip_if_not(file.exists(surface_file), message="Test data missing.");
 
@@ -60,8 +60,8 @@ test_that("The vertices of a face are close to each other", {
 
   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");
+  freesurferformats::download_opt_data();
+  subjects_dir = freesurferformats::get_opt_data_filepath("subjects_dir");
   surface_file = file.path(subjects_dir, "subject1", "surf", "lh.white");
   skip_if_not(file.exists(surface_file), message="Test data missing.");
 
diff --git a/tests/testthat/test-write-fs-surface.R b/tests/testthat/test-write-fs-surface.R
index c2a72a6..b94d846 100644
--- a/tests/testthat/test-write-fs-surface.R
+++ b/tests/testthat/test-write-fs-surface.R
@@ -39,8 +39,8 @@ 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");
+  freesurferformats::download_opt_data();
+  subjects_dir = freesurferformats::get_opt_data_filepath("subjects_dir");
   surface_file = file.path(subjects_dir, "subject1", "surf", "lh.white");
 
   skip_if_not(file.exists(surface_file), message="Test data missing.");