diff --git a/test_s3.py b/test_s3.py
index e143ef4..18156ec 100644
--- a/test_s3.py
+++ b/test_s3.py
@@ -1000,3 +1000,76 @@ def test_100_continue():
 
     status = _simple_http_req_100_cont(s3.main.host, s3.main.port, 'PUT', resource)
     eq(status, '100')
+
+def _test_atomic_write(file_size):
+    bucket = get_new_bucket()
+    objname = 'testobj'
+    key = bucket.new_key(objname)
+
+    class FakeFile(object):
+        def __init__(self, size, char='A', interrupt=None):
+            self.offset = 0
+            self.size = size
+            self.char = char
+            self.interrupt = interrupt
+
+        def seek(self, offset):
+            self.offset = offset
+
+        def tell(self):
+            return self.offset
+
+        def read(self, size=-1):
+            if size < 0:
+                size = self.size - self.offset
+            count = min(size, self.size - self.offset)
+            self.offset += count
+
+            # Sneaky! do stuff before we return (the last time)
+            if self.interrupt != None and self.offset == self.size:
+                self.interrupt()
+
+            return self.char*count
+
+    class FakeFileVerifier(object):
+        def __init__(self, char=None):
+            self.char = char
+            self.size = 0
+
+        def write(self, data):
+            size = len(data)
+            if self.char == None:
+                self.char = data[0]
+            self.size += size
+            eq(data, self.char*size)
+   
+    # create <file_size> file of A's
+    fp_a = FakeFile(file_size, 'A')
+    key.set_contents_from_file(fp_a)
+    
+    # verify A's
+    fp_a_verify = FakeFileVerifier('A')
+    key.get_contents_to_file(fp_a_verify)
+    eq(fp_a_verify.size, file_size)
+
+    # create <file_size> file of B's
+    # but try to verify the file before we finish writing all the B's
+    fp_b = FakeFile(file_size, 'B',
+        lambda: key.get_contents_to_file(FakeFileVerifier())
+        )
+    key.set_contents_from_file(fp_b)
+
+    # verify B's
+    fp_b_verify = FakeFileVerifier('B')
+    key.get_contents_to_file(fp_b_verify)
+    eq(fp_b_verify.size, file_size)
+
+def test_atomic_write_1mb():
+    _test_atomic_write(1024*1024)
+
+def test_atomic_write_4mb():
+    _test_atomic_write(1024*1024*4)
+
+def test_atomic_write_8mb():
+    _test_atomic_write(1024*1024*8)
+