diff --git a/imas/backends/imas_core/mdsplus_model.py b/imas/backends/imas_core/mdsplus_model.py
index 48864346..3c91cefb 100644
--- a/imas/backends/imas_core/mdsplus_model.py
+++ b/imas/backends/imas_core/mdsplus_model.py
@@ -12,7 +12,6 @@
 import time
 import uuid
 from pathlib import Path
-from saxonche import PySaxonProcessor
 from subprocess import CalledProcessError, check_output
 from zlib import crc32
 
@@ -244,11 +243,20 @@ def transform_with_xslt(xslt_processor, source, xslfile, output_file):
 
 def create_model_ids_xml(cache_dir_path, fname, version):
     """Use Saxon/C to compile an ids.xml suitable for creating an MDSplus model."""
+    try:
+        import saxonche
+    except ImportError:
+        raise RuntimeError(
+            "Building mdsplus models requires the 'saxonche' python package. "
+            "Please install this package (for example with 'pip install saxonche') "
+            "and try again."
+        )
+
     try:
         with as_file(files("imas") / "assets" / "IDSDef2MDSpreTree.xsl") as xslfile:
             output_file = Path(cache_dir_path) / "ids.xml"
 
-            with PySaxonProcessor(license=False) as proc:
+            with saxonche.PySaxonProcessor(license=False) as proc:
                 xslt_processor = proc.new_xslt30_processor()
                 xdm_ddgit = proc.make_string_value(str(version) or fname)
                 xslt_processor.set_parameter("DD_GIT_DESCRIBE", xdm_ddgit)
diff --git a/pyproject.toml b/pyproject.toml
index 6134366c..066e0ea9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,7 +1,7 @@
 [build-system]
 # Minimum requirements for the build system to execute.
 # Keep this on a single line for the grep magic of build scripts to work
-requires = ["setuptools>=61", "wheel", "numpy", "gitpython", "saxonche","packaging", "tomli;python_version<'3.11'", "setuptools_scm>8"]
+requires = ["setuptools>=61", "wheel", "numpy", "packaging", "tomli;python_version<'3.11'", "setuptools_scm>8"]
 
 build-backend = "setuptools.build_meta"
 
@@ -63,8 +63,6 @@ dependencies = [
     "importlib_resources;python_version<'3.9'",
     "packaging",
     "xxhash >= 2",
-    "saxonche",
-    "gitpython",
     "imas_data_dictionaries",
 ]
 
@@ -92,6 +90,9 @@ h5py = [
 xarray = [
     "xarray",
 ]
+saxonche = [
+    "saxonche",
+]
 test = [
     "pytest>=5.4.1",
     "pytest-cov>=0.6",
@@ -101,11 +102,11 @@ test = [
     "asv == 0.6.1",
     # virtualenv is a dependency of asv
     "virtualenv",
-    # Pint and xarray are used in training snippets
+    # Pint is used in training snippets
     "pint",
     # Optional dependencies
     # TODO add imas-core when it is available on pypi
-    "imas-python[netcdf,h5py,xarray]",
+    "imas-python[netcdf,h5py,xarray,saxonche]",
 ]
 
 [project.scripts]