diff --git a/dvc/remote/hdfs.py b/dvc/remote/hdfs.py
index ec37ace63..efdbfbba4 100644
--- a/dvc/remote/hdfs.py
+++ b/dvc/remote/hdfs.py
@@ -143,6 +143,8 @@ class RemoteHDFS(RemoteBASE):
 
     @contextmanager
     def open(self, path_info, mode="r", encoding=None):
+        assert mode in {"r", "rt", "rb"}
+
         try:
             with self.hdfs(path_info) as hdfs, closing(
                 hdfs.open(path_info.path, mode="rb")
diff --git a/dvc/repo/__init__.py b/dvc/repo/__init__.py
index af9d7a92f..2f743a6ff 100644
--- a/dvc/repo/__init__.py
+++ b/dvc/repo/__init__.py
@@ -440,8 +440,6 @@ class Repo(object):
     @contextmanager
     def open(self, path, remote=None, mode="r", encoding=None):
         """Opens a specified resource as a file descriptor"""
-        assert mode in {"r", "rt", "rb"}
-
         try:
             with self._open(path, remote, mode, encoding) as fd:
                 yield fd
diff --git a/dvc/utils/http.py b/dvc/utils/http.py
index 7d8c6f55a..b2ecf4bb3 100644
--- a/dvc/utils/http.py
+++ b/dvc/utils/http.py
@@ -13,6 +13,8 @@ def open_url(url, mode="r", encoding=None):
     Resumes on connection error.
     Url could be a string or a callable returning a string.
     """
+    assert mode in {"r", "rt", "rb"}
+
     with iter_url(url) as (response, it):
         bytes_stream = IterStream(it)