diff --git a/dandi/keyring.py b/dandi/keyring.py
index 99cc0767e..cc0579644 100644
--- a/dandi/keyring.py
+++ b/dandi/keyring.py
@@ -110,6 +110,7 @@ def keyring_op(
             len(kbs) == 1
         ), "EncryptedKeyring not available; is pycryptodomex installed?"
         kb = kbs[0]
+        assert isinstance(kb, EncryptedKeyring)
         if op.exists(kb.file_path):
             lgr.info("EncryptedKeyring file exists; using as keyring backend")
             return (kb, func(kb))
diff --git a/dandi/tests/fixtures.py b/dandi/tests/fixtures.py
index 2ad4505ab..a13fa954b 100644
--- a/dandi/tests/fixtures.py
+++ b/dandi/tests/fixtures.py
@@ -656,19 +656,17 @@ def video_files(tmp_path: Path) -> list[tuple[Path, Path]]:
         (nf, nx, ny) = (2, 2, 2)
         writer1 = cv2.VideoWriter(
             filename=str(movie_file1),
-            apiPreference=None,
-            fourcc=cv2.VideoWriter_fourcc(*"DIVX"),
-            fps=25,
+            apiPreference=0,
+            fourcc=cv2.VideoWriter.fourcc(*"DIVX"),
+            fps=25.0,
             frameSize=(ny, nx),
-            params=None,
         )
         writer2 = cv2.VideoWriter(
             filename=str(movie_file2),
-            apiPreference=None,
-            fourcc=cv2.VideoWriter_fourcc(*"DIVX"),
+            apiPreference=0,
+            fourcc=cv2.VideoWriter.fourcc(*"DIVX"),
             fps=25,
             frameSize=(ny, nx),
-            params=None,
         )
         for k in range(nf):
             writer1.write(np.random.randint(0, 255, (nx, ny, 3)).astype("uint8"))