diff --git a/doc/whats-new.rst b/doc/whats-new.rst
index 25c14d4de6a..fc18da854af 100644
--- a/doc/whats-new.rst
+++ b/doc/whats-new.rst
@@ -100,6 +100,8 @@ Enhancements
 Bug fixes
 ~~~~~~~~~
 
+- Fix ``isnull()`` to account for changes with pandas 0.21.
+
 - :py:func:`~xarray.open_rasterio` method now shifts the rasterio
   coordinates so that they are centered in each pixel.
   By `Greg Brener <https://github.com/gbrener>`_.
@@ -2032,4 +2034,4 @@ Miles.
 v0.1 (2 May 2014)
 -----------------
 
-Initial release.
\ No newline at end of file
+Initial release.
diff --git a/xarray/core/ops.py b/xarray/core/ops.py
index b840f26073c..c6e2667bc8e 100644
--- a/xarray/core/ops.py
+++ b/xarray/core/ops.py
@@ -319,7 +319,7 @@ def inject_all_ops_and_reduce_methods(cls, priority=50, array_only=True):
         setattr(cls, name, cls._unary_op(_method_wrapper(name)))
 
     for name in PANDAS_UNARY_FUNCTIONS:
-        f = _func_slash_method_wrapper(getattr(pd, name))
+        f = _func_slash_method_wrapper(getattr(pd, name), name=name)
         setattr(cls, name, cls._unary_op(f))
 
     f = _func_slash_method_wrapper(duck_array_ops.around, name='round')