diff --git a/debugger_protocol/schema/__main__.py b/debugger_protocol/schema/__main__.py
index 773502de..fb9817a6 100644
--- a/debugger_protocol/schema/__main__.py
+++ b/debugger_protocol/schema/__main__.py
@@ -24,7 +24,7 @@ def handle_download(source=UPSTREAM, target=VENDORED, *,
     with _open_url(source) as infile:
         with _open(target, 'wb') as outfile:
             meta = download(source, infile, outfile,
-                            _open=_open)
+                            _open_url=_open_url)
 
     # Save the metadata.
     metafile, _ = open_metadata(target, 'w',
diff --git a/debugger_protocol/schema/_util.py b/debugger_protocol/schema/_util.py
index a0bb544f..dbb70781 100644
--- a/debugger_protocol/schema/_util.py
+++ b/debugger_protocol/schema/_util.py
@@ -9,10 +9,10 @@ def open_url(url):
     return urllib.request.urlopen(url)
 
 
-def get_revision(url, *, _open=open_url):
+def get_revision(url, *, _open_url=open_url):
     """Return the revision corresponding to the given URL."""
     if url.startswith('https://github.com/'):
-        return github_get_revision(url, _open=_open)
+        return github_get_revision(url, _open_url=_open_url)
     else:
         raise NotImplementedError
 
@@ -35,7 +35,7 @@ GH_RESOURCE_RE = re.compile(r'^https://github.com'
                             r'/(?P<path>.*)$')
 
 
-def github_get_revision(url, *, _open=open_url):
+def github_get_revision(url, *, _open_url=open_url):
     """Return the full commit hash corresponding to the given URL."""
     m = GH_RESOURCE_RE.match(url)
     if not m:
@@ -44,7 +44,7 @@ def github_get_revision(url, *, _open=open_url):
 
     revurl = ('https://api.github.com/repos/{}/{}/commits/{}'
               ).format(org, repo, ref)
-    with _open(revurl) as revinfo:
+    with _open_url(revurl) as revinfo:
         raw = revinfo.read()
     data = json.loads(raw.decode())
     return data['sha']
diff --git a/debugger_protocol/schema/upstream.py b/debugger_protocol/schema/upstream.py
index b46a057d..db40f27e 100644
--- a/debugger_protocol/schema/upstream.py
+++ b/debugger_protocol/schema/upstream.py
@@ -10,10 +10,11 @@ from .metadata import Metadata
 URL = 'https://github.com/Microsoft/vscode-debugadapter-node/raw/master/debugProtocol.json'  # noqa
 
 
-def download(source, infile, outfile, *, _now=datetime.utcnow, _open=open_url):
+def download(source, infile, outfile, *,
+             _now=datetime.utcnow, _open_url=open_url):
     """Return the corresponding metadata after downloading the schema file."""
     timestamp = _now()
-    revision = get_revision(source, _open=_open)
+    revision = get_revision(source, _open_url=_open_url)
 
     data = infile.read()
     checksum = get_checksum(data)
@@ -31,5 +32,5 @@ def read(url, *, _open_url=open_url):
         # TODO: Ensure it's a 404 error?
         raise SchemaFileError('schema file at {!r} not found'.format(url))
     with infile:
-        upstream = download(url, infile, outfile, _open=_open_url)
+        upstream = download(url, infile, outfile, _open_url=_open_url)
     return outfile.getvalue(), upstream
diff --git a/tests/debugger_protocol/schema/test_upstream.py b/tests/debugger_protocol/schema/test_upstream.py
index 39b100b5..75c6503a 100644
--- a/tests/debugger_protocol/schema/test_upstream.py
+++ b/tests/debugger_protocol/schema/test_upstream.py
@@ -21,7 +21,7 @@ class DownloadTests(unittest.TestCase):
                         infile,
                         outfile,
                         _now=(lambda: now),
-                        _open=(lambda _: buf),
+                        _open_url=(lambda _: buf),
                         )
         rcvd = outfile.getvalue()
 
diff --git a/tests/debugger_protocol/schema/test_util.py b/tests/debugger_protocol/schema/test_util.py
index d24a265e..e048105c 100644
--- a/tests/debugger_protocol/schema/test_util.py
+++ b/tests/debugger_protocol/schema/test_util.py
@@ -10,7 +10,7 @@ class GetRevisionTests(unittest.TestCase):
         buf = io.BytesIO(
                 b'{"sha": "fc2395ca3564fb2afded8d90ddbe38dad1bf86f1"}')
         revision = get_revision('https://github.com/x/y/raw/master/z',
-                                _open=lambda _: buf)
+                                _open_url=lambda _: buf)
 
         self.assertEqual(revision, 'fc2395ca3564fb2afded8d90ddbe38dad1bf86f1')