Index: breathe-4.35.0/tests/test_renderer.py
===================================================================
--- breathe-4.35.0.orig/tests/test_renderer.py
+++ breathe-4.35.0/tests/test_renderer.py
@@ -35,7 +35,11 @@ def app(test_params, app_params, make_ap
     """
     args, kwargs = app_params
     assert "srcdir" in kwargs
-    kwargs["srcdir"].makedirs(exist_ok=True)
+    try:
+        kwargs["srcdir"].mkdir(parents=True, exist_ok=True)
+    except AttributeError:
+        # old version of Sphinx
+        kwargs["srcdir"].makedirs(exist_ok=True)
     (kwargs["srcdir"] / "conf.py").write_text("")
     app_ = make_app(*args, **kwargs)
     yield app_
Index: breathe-4.35.0/breathe/project.py
===================================================================
--- breathe-4.35.0.orig/breathe/project.py
+++ breathe-4.35.0/breathe/project.py
@@ -113,7 +113,7 @@ class ProjectInfoFactory:
         # Assume general build directory is the doctree directory without the last component.
         # We strip off any trailing slashes so that dirname correctly drops the last part.
         # This can be overridden with the breathe_build_directory config variable
-        self._default_build_dir = os.path.dirname(app.doctreedir.rstrip(os.sep))
+        self._default_build_dir = app.doctreedir.parent
         self.project_count = 0
         self.project_info_store: Dict[str, ProjectInfo] = {}
         self.project_info_for_auto_store: Dict[str, AutoProjectInfo] = {}