diff --git a/zarr/storage.py b/zarr/storage.py
index 8b387ed1f8..670fd62a3e 100644
--- a/zarr/storage.py
+++ b/zarr/storage.py
@@ -34,6 +34,8 @@
 from threading import Lock, RLock
 import uuid
 
+import numpy
+
 from numcodecs.compat import ensure_bytes, ensure_contiguous_ndarray
 from numcodecs.registry import codec_registry
 
@@ -740,8 +742,7 @@ def __init__(self, path):
     def __getitem__(self, key):
         filepath = os.path.join(self.path, key)
         if os.path.isfile(filepath):
-            with open(filepath, 'rb') as f:
-                return f.read()
+            return numpy.fromfile(filepath, dtype='u1')
         else:
             raise KeyError(key)
 
@@ -773,8 +774,7 @@ def __setitem__(self, key, value):
         temp_name = file_name + '.' + uuid.uuid4().hex + '.partial'
         temp_path = os.path.join(dir_path, temp_name)
         try:
-            with open(temp_path, mode='wb') as f:
-                f.write(value)
+            value.tofile(temp_path)
 
             # move temporary file into place
             replace(temp_path, file_path)