diff --git a/changelog.d/3336.misc.rst b/changelog.d/3336.misc.rst
new file mode 100644
index 0000000000..288b1eb3ac
--- /dev/null
+++ b/changelog.d/3336.misc.rst
@@ -0,0 +1 @@
+Modified ``test_setup_install_includes_dependencies`` to work with custom ``PYTHONPATH`` –- by :user:`hroncok`
\ No newline at end of file
diff --git a/setuptools/tests/test_easy_install.py b/setuptools/tests/test_easy_install.py
index 726f9fda5a..73a8dfff08 100644
--- a/setuptools/tests/test_easy_install.py
+++ b/setuptools/tests/test_easy_install.py
@@ -474,22 +474,27 @@ def test_setup_install_includes_dependencies(self, tmp_path, mock_index):
             '--install-purelib', str(install_root),
             '--install-platlib', str(install_root),
         ]
-        env = {"PYTHONPATH": str(install_root), "__EASYINSTALL_INDEX": mock_index.url}
-        with pytest.raises(subprocess.CalledProcessError) as exc_info:
-            subprocess.check_output(
-                cmd, cwd=str(project_root), env=env, stderr=subprocess.STDOUT, text=True
-            )
+        env = {**os.environ, "__EASYINSTALL_INDEX": mock_index.url}
+        cp = subprocess.run(
+            cmd,
+            cwd=str(project_root),
+            env=env,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.STDOUT,
+            text=True,
+        )
+        assert cp.returncode != 0
         try:
             assert '/does-not-exist/' in {r.path for r in mock_index.requests}
             assert next(
                 line
-                for line in exc_info.value.output.splitlines()
+                for line in cp.stdout.splitlines()
                 if "not find suitable distribution for" in line
                 and "does-not-exist" in line
             )
         except Exception:
-            if "failed to get random numbers" in exc_info.value.output:
-                pytest.xfail(f"{sys.platform} failure - {exc_info.value.output}")
+            if "failed to get random numbers" in cp.stdout:
+                pytest.xfail(f"{sys.platform} failure - {cp.stdout}")
             raise
 
     def create_project(self, root):