diff --git a/xarray/backends/pynio_.py b/xarray/backends/pynio_.py
index 075db5d4ccb..cf792bb699a 100644
--- a/xarray/backends/pynio_.py
+++ b/xarray/backends/pynio_.py
@@ -3,6 +3,7 @@
 from __future__ import print_function
 
 import functools
+import contextlib
 
 import numpy as np
 
@@ -21,16 +22,18 @@ def __init__(self, variable_name, datastore):
 
     @property
     def array(self):
-        return self.datastore.ds.variables[self.variable_name]
+        with self.datastore.ensure_open():
+            return self.datastore.ds.variables[self.variable_name]
 
     @property
     def dtype(self):
         return np.dtype(self.array.typecode())
 
     def __getitem__(self, key):
-        if key == () and self.ndim == 0:
-            return self.array.get_value()
-        return self.array[key]
+        with self.datastore.ensure_open():
+            if key == () and self.ndim == 0:
+                return self.array.get_value()
+            return self.array[key]
 
 
 class NioDataStore(AbstractDataStore, DataStorePickleMixin):
@@ -40,22 +43,34 @@ def __init__(self, filename, mode='r'):
         import Nio
         opener = functools.partial(Nio.open_file, filename, mode=mode)
         self.ds = opener()
+        self._isopen = True
         self._opener = opener
         self._mode = mode
 
+    @contextlib.contextmanager
+    def ensure_open(self):
+        if not self._isopen:
+            self.ds = self._opener()
+            self._isopen = True
+        yield
+
     def open_store_variable(self, name, var):
         data = indexing.LazilyIndexedArray(NioArrayWrapper(name, self))
         return Variable(var.dimensions, data, var.attributes)
 
     def get_variables(self):
-        return FrozenOrderedDict((k, self.open_store_variable(k, v))
-                                 for k, v in self.ds.variables.iteritems())
+        with self.ensure_open():
+            return FrozenOrderedDict((k, self.open_store_variable(k, v))
+                                     for k, v in self.ds.variables.iteritems())
 
     def get_attrs(self):
-        return Frozen(self.ds.attributes)
+        with self.ensure_open():
+            return Frozen(self.ds.attributes)
 
     def get_dimensions(self):
-        return Frozen(self.ds.dimensions)
+        with self.ensure_open():
+            return Frozen(self.ds.dimensions)
 
     def close(self):
+        self._isopen = False
         self.ds.close()