diff -ruN a/pdm/pep517/base.py b/pdm/pep517/base.py
--- a/pdm/pep517/base.py	2022-07-10 07:00:32.663631000 +0200
+++ b/pdm/pep517/base.py	2022-07-21 10:42:50.692079277 +0200
@@ -6,7 +6,7 @@
 from pathlib import Path
 from typing import Any, Dict, Iterator, List, Mapping, Optional, Tuple, TypeVar, Union
 
-from pdm.pep517._vendor import tomli
+import tomli
 from pdm.pep517.exceptions import MetadataError, PDMWarning, ProjectError
 from pdm.pep517.metadata import Metadata
 from pdm.pep517.utils import is_python_package, safe_version, to_filename
diff -ruN a/pdm/pep517/license.py b/pdm/pep517/license.py
--- a/pdm/pep517/license.py	2022-07-10 07:00:32.663631000 +0200
+++ b/pdm/pep517/license.py	2022-07-21 10:41:41.322359486 +0200
@@ -1,6 +1,6 @@
 import warnings
 
-from pdm.pep517._vendor.license_expression import (
+from license_expression import (
     LicenseSymbol,
     Licensing,
     get_spdx_licensing,
diff -ruN a/pdm/pep517/metadata.py b/pdm/pep517/metadata.py
--- a/pdm/pep517/metadata.py	2022-07-10 07:00:32.663631000 +0200
+++ b/pdm/pep517/metadata.py	2022-07-21 10:43:29.681922662 +0200
@@ -16,7 +16,7 @@
     cast,
 )
 
-from pdm.pep517._vendor.packaging.requirements import Requirement
+from packaging.requirements import Requirement
 from pdm.pep517.exceptions import MetadataError, PDMWarning, ProjectError
 from pdm.pep517.license import normalize_expression
 from pdm.pep517.utils import (
diff -ruN a/pdm/pep517/scm.py b/pdm/pep517/scm.py
--- a/pdm/pep517/scm.py	2022-07-10 07:00:32.663631000 +0200
+++ b/pdm/pep517/scm.py	2022-07-21 10:43:11.761994569 +0200
@@ -11,8 +11,8 @@
 from datetime import datetime
 from typing import Any, Dict, Iterable, List, NamedTuple, Optional, Tuple, Union
 
-from pdm.pep517._vendor.packaging.version import LegacyVersion, Version
-from pdm.pep517._vendor.packaging.version import parse as parse_version
+from packaging.version import LegacyVersion, Version
+from packaging.version import parse as parse_version
 
 DEFAULT_TAG_REGEX = re.compile(
     r"^(?:[\w-]+-)?(?P<version>[vV]?\d+(?:\.\d+){0,2}[^\+]*)(?:\+.*)?$"
diff -ruN a/pdm/pep517/sdist.py b/pdm/pep517/sdist.py
--- a/pdm/pep517/sdist.py	2022-07-10 07:00:32.663631000 +0200
+++ b/pdm/pep517/sdist.py	2022-07-21 10:41:22.852434458 +0200
@@ -6,7 +6,8 @@
 from copy import copy
 from typing import Any, Iterator
 
-from pdm.pep517._vendor import tomli, tomli_w
+import tomli
+import tomli_w
 from pdm.pep517.base import Builder
 
 
diff -ruN a/pdm/pep517/utils.py b/pdm/pep517/utils.py
--- a/pdm/pep517/utils.py	2022-07-10 07:00:32.663631000 +0200
+++ b/pdm/pep517/utils.py	2022-07-21 10:42:32.178820523 +0200
@@ -9,10 +9,10 @@
 from pathlib import Path
 from typing import Callable, Generator, Iterable, Optional, Type, Union
 
-from pdm.pep517._vendor.packaging import tags
-from pdm.pep517._vendor.packaging.markers import Marker
-from pdm.pep517._vendor.packaging.requirements import InvalidRequirement, Requirement
-from pdm.pep517._vendor.packaging.version import InvalidVersion, Version
+from packaging import tags
+from packaging.markers import Marker
+from packaging.requirements import InvalidRequirement, Requirement
+from packaging.version import InvalidVersion, Version
 from pdm.pep517.exceptions import MetadataError
 from pdm.pep517.macosx_platform import calculate_macosx_platform_tag
 
diff -ruN a/pdm/pep517/validator.py b/pdm/pep517/validator.py
--- a/pdm/pep517/validator.py	2022-07-10 07:00:32.663631000 +0200
+++ b/pdm/pep517/validator.py	2022-07-21 10:40:22.092682287 +0200
@@ -1,6 +1,6 @@
 from typing import Mapping
 
-from pdm.pep517._vendor import cerberus
+import cerberus
 from pdm.pep517.exceptions import PEP621ValidationError
 
 README_RULE = [
diff -ruN a/pdm/pep517/wheel.py b/pdm/pep517/wheel.py
--- a/pdm/pep517/wheel.py	2022-07-10 07:00:32.663631000 +0200
+++ b/pdm/pep517/wheel.py	2022-07-21 10:40:53.322554669 +0200
@@ -16,8 +16,8 @@
 from typing import Any, Dict, Generator, List, Mapping, Optional, TextIO, Tuple, Union
 
 from pdm.pep517 import __version__
-from pdm.pep517._vendor.packaging import tags
-from pdm.pep517._vendor.packaging.specifiers import SpecifierSet
+from packaging import tags
+from packaging.specifiers import SpecifierSet
 from pdm.pep517.base import Builder
 from pdm.pep517.exceptions import BuildError, PDMWarning
 from pdm.pep517.utils import get_abi_tag, get_platform, show_warning
diff -ruN a/pyproject.toml b/pyproject.toml
--- a/pyproject.toml	2022-07-10 07:00:32.663631000 +0200
+++ b/pyproject.toml	2022-07-21 10:46:41.084494800 +0200
@@ -21,7 +21,13 @@
     "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
 ]
-dependencies = []
+dependencies = [
+    "cerberus",
+    "license-expression",
+    "packaging",
+    "tomli",
+    "tomli-w",
+]
 version = "1.0.2"
 
 [project.license]
diff -ruN a/tests/test_metadata.py b/tests/test_metadata.py
--- a/tests/test_metadata.py	2022-07-10 07:00:32.667631100 +0200
+++ b/tests/test_metadata.py	2022-07-21 10:42:05.778927122 +0200
@@ -5,7 +5,7 @@
 
 import pytest
 
-from pdm.pep517._vendor import tomli
+import tomli
 from pdm.pep517.metadata import Metadata
 from tests import FIXTURES
 
