diff --git a/intake_xarray/opendap.py b/intake_xarray/opendap.py
index 2a40709..a2e8423 100644
--- a/intake_xarray/opendap.py
+++ b/intake_xarray/opendap.py
@@ -22,7 +22,7 @@ class OpenDapSource(DataSourceMixin):
     ----------
     urlpath: str
         Path to source file.
-    chunks: int or dict
+    chunks: None, int or dict
         Chunks is used to load the new dataset into dask
         arrays. ``chunks={}`` loads the dataset with dask using a single
         chunk for all arrays.
@@ -39,7 +39,7 @@ class OpenDapSource(DataSourceMixin):
     """
     name = 'opendap'
 
-    def __init__(self, urlpath, chunks, auth=None, xarray_kwargs=None, metadata=None,
+    def __init__(self, urlpath, chunks=None, auth=None, xarray_kwargs=None, metadata=None,
                  **kwargs):
         self.urlpath = urlpath
         self.chunks = chunks