diff --git a/pip_api/__init__.py b/pip_api/__init__.py
index 28e3372..77f9d47 100644
--- a/pip_api/__init__.py
+++ b/pip_api/__init__.py
@@ -8,6 +8,7 @@
 
 PIP_VERSION: Version = packaging_version.parse(version())  # type: ignore
 PYTHON_VERSION = sys.version_info
+VENDORED = False
 
 # Import these because they depend on the above
 from pip_api._hash import hash
diff --git a/pip_api/_hash.py b/pip_api/_hash.py
index e02944f..cf4ee2e 100644
--- a/pip_api/_hash.py
+++ b/pip_api/_hash.py
@@ -19,8 +19,12 @@ def hash(filename: os.PathLike, algorithm: str = "sha256") -> str:
     if algorithm not in ["sha256", "sha384", "sha512"]:
         raise InvalidArguments("Algorithm {} not supported".format(algorithm))
 
-    result = call("hash", "--algorithm", algorithm, filename)
-
-    # result is of the form:
-    # <filename>:\n--hash=<algorithm>:<hash>\n
-    return result.strip().split(":")[-1]
+    if pip_api.VENDORED:
+        from pip._internal.commands.hash import _hash_of_file
+
+        return _hash_of_file(str(filename), algorithm)
+    else:
+        result = call("hash", "--algorithm", algorithm, filename)
+        # result is of the form:
+        # <filename>:\n--hash=<algorithm>:<hash>\n
+        return result.strip().split(":")[-1]
diff --git a/tests/conftest.py b/tests/conftest.py
index 264d5f6..6c10959 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -8,7 +8,7 @@
 
 from pip_api._vendor.packaging.version import Version
 
-import pip_api
+import pip_api as _pip_api
 
 
 @pytest.fixture
@@ -127,7 +127,7 @@ def __init__(self):
         # Install the right version of pip. By default,
         # virtualenv gets the version from the wheels that
         # are bundled along with it
-        self.run("install", "pip=={}".format(str(pip_api.PIP_VERSION)))
+        self.run("install", "pip=={}".format(str(_pip_api.PIP_VERSION)))
 
     def run(self, *args):
         python_location = os.environ["PIPAPI_PYTHON_LOCATION"]
@@ -145,3 +145,9 @@ def pip(tmpdir, venv):
     ``tests.lib.scripttest.PipTestEnvironment``.
     """
     return PipTestEnvironment()
+
+
+@pytest.fixture(params=[True, False])
+def pip_api(request, monkeypatch):
+    monkeypatch.setattr(_pip_api, "VENDORED", request.param)
+    return _pip_api
diff --git a/tests/test_hash.py b/tests/test_hash.py
index a33af29..f8e1acf 100644
--- a/tests/test_hash.py
+++ b/tests/test_hash.py
@@ -1,13 +1,6 @@
 import pytest
 
-import pip_api
 
-xfail_incompatible = pytest.mark.xfail(
-    pip_api._hash.incompatible, reason="Incompatible"
-)
-
-
-@xfail_incompatible
 @pytest.mark.parametrize(
     "algorithm, expected",
     [
@@ -22,20 +15,27 @@
         ),
     ],
 )
-def test_hash(some_distribution, algorithm, expected):
+def test_hash(some_distribution, algorithm, expected, pip_api):
+    if pip_api._hash.incompatible:
+        pytest.xfail("Incompatible")
+
     result = pip_api.hash(some_distribution.filename, algorithm=algorithm)
 
     assert result == expected
 
 
-@xfail_incompatible
-def test_hash_default_algorithm_is_256(some_distribution):
+def test_hash_default_algorithm_is_256(some_distribution, pip_api):
+    if pip_api._hash.incompatible:
+        pytest.xfail("Incompatible")
+
     sha256 = "cce4031ec744585688ddab649427133ac22396da29ad82fdbd11692c3a26fe19"
 
     assert pip_api.hash(some_distribution.filename) == sha256
 
 
-@xfail_incompatible
-def test_hash_invalid_algorithm():
+def test_hash_invalid_algorithm(pip_api):
+    if pip_api._hash.incompatible:
+        pytest.xfail("Incompatible")
+
     with pytest.raises(pip_api.exceptions.InvalidArguments):
         pip_api.hash("whatever", "invalid")