diff --git a/src/pip/_internal/operations/install/wheel.py b/src/pip/_internal/operations/install/wheel.py
index e7315ee4..4e36b03d 100644
--- a/src/pip/_internal/operations/install/wheel.py
+++ b/src/pip/_internal/operations/install/wheel.py
@@ -615,6 +615,8 @@ def install_wheel(
     direct_url=None,  # type: Optional[DirectUrl]
 ):
     # type: (...) -> None
+    _temp_dir_for_testing = (
+        _temp_dir_for_testing or os.environ.get("NIX_PIP_INSTALL_TMPDIR"))
     with TempDirectory(
         path=_temp_dir_for_testing, kind="unpacked-wheel"
     ) as unpacked_dir, ZipFile(wheel_path, allowZip64=True) as z: