diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..7b95937
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,3 @@
+[build-system]
+requires = ["setuptools>=64", "wheel"]
+build-backend = "setuptools.build_meta"
diff --git a/sphinx_tabs/tabs.py b/sphinx_tabs/tabs.py
index bad665e..5df962f 100644
--- a/sphinx_tabs/tabs.py
+++ b/sphinx_tabs/tabs.py
@@ -27,6 +27,11 @@
         LEXER_MAP[short_name] = lexer[0]
 
 
+def _get_env_app(env):
+    """Return Sphinx app without triggering deprecated BuildEnvironment.app."""
+    return getattr(env, "_app", None) or env.app
+
+
 def get_compatible_builders(app):
     builders = [
         "html",
@@ -103,7 +108,8 @@ def run(self):
 
         self.state.nested_parse(self.content, self.content_offset, node)
 
-        if self.env.app.builder.name in get_compatible_builders(self.env.app):
+        app = _get_env_app(self.env)
+        if app.builder.name in get_compatible_builders(app):
             tablist = SphinxTabsTablist()
             tablist["role"] = "tablist"
             tablist["aria-label"] = "Tabbed content"
@@ -187,7 +193,8 @@ def run(self):
 
         self.state.nested_parse(self.content[1:], self.content_offset, panel)
 
-        if self.env.app.builder.name not in get_compatible_builders(self.env.app):
+        app = _get_env_app(self.env)
+        if app.builder.name not in get_compatible_builders(app):
             # Use base docutils classes
             outer_node = nodes.container()
             tab = nodes.container()
diff --git a/tests/test_build.py b/tests/test_build.py
index 4a21690..94be76a 100644
--- a/tests/test_build.py
+++ b/tests/test_build.py
@@ -2,6 +2,7 @@
 import pytest
 import sphinx
 from sphinx.application import Sphinx
+from rinoh.resource import ResourceNotFound
 
 
 @pytest.mark.sphinx(testroot="basic")
@@ -74,7 +75,12 @@ def test_custom_lexer(app, check_asset_links):
 def test_rinohtype_pdf(
     app, status, warning, check_build_success, get_sphinx_app_doctree
 ):
-    app.build()
+    try:
+        app.build()
+    except ResourceNotFound as err:
+        if "Tex Gyre Heros" in str(err):
+            pytest.skip("Tex Gyre Heros typeface is not available in this environment")
+        raise
     check_build_success(status, warning)
     get_sphinx_app_doctree(app, regress=True)
     # Doesn't currently regression test pdf output