diff --git a/src/calibre/utils/zipfile.py b/src/calibre/utils/zipfile.py
index 6bf6f2f83c..9943119968 100644
--- a/src/calibre/utils/zipfile.py
+++ b/src/calibre/utils/zipfile.py
@@ -6,8 +6,8 @@ from __future__ import with_statement
 import struct, os, time, sys, shutil
 import binascii, cStringIO
 from contextlib import closing
+from tempfile import SpooledTemporaryFile
 
-from calibre.ptempfile import TemporaryDirectory
 from calibre import sanitize_file_name
 from calibre.constants import filesystem_encoding
 from calibre.ebooks.chardet import detect
@@ -467,6 +467,7 @@ class ZipExtFile:
 
     def __init__(self, fileobj, zipinfo, decrypt=None):
         self.fileobj = fileobj
+        self.orig_pos = fileobj.tell()
         self.decrypter = decrypt
         self.bytes_read = 0L
         self.rawbuffer = ''
@@ -582,6 +583,20 @@ class ZipExtFile:
             result.append(line)
         return result
 
+    def read_raw(self):
+        pos = self.fileobj.tell()
+        self.fileobj.seek(self.orig_pos)
+        bytes_to_read = self.compress_size
+        if self.decrypter is not None:
+            bytes_to_read -= 12
+        raw = b''
+
+        if bytes_to_read > 0:
+            raw = self.fileobj.read(bytes_to_read)
+        self.fileobj.seek(pos)
+        return raw
+
+
     def read(self, size = None):
         # act like file() obj and return empty string if size is 0
         if size == 0:
@@ -925,6 +940,11 @@ class ZipFile:
         """Return file bytes (as a string) for name."""
         return self.open(name, "r", pwd).read()
 
+    def read_raw(self, name, mode="r", pwd=None):
+        """Return the raw bytes in the zipfile corresponding to name."""
+        zef = self.open(name, mode=mode, pwd=pwd)
+        return zef.read_raw()
+
     def open(self, name, mode="r", pwd=None):
         """Return file-like object for 'name'."""
         if mode not in ("r", "U", "rU"):
@@ -1159,10 +1179,13 @@ class ZipFile:
         self.filelist.append(zinfo)
         self.NameToInfo[zinfo.filename] = zinfo
 
-    def writestr(self, zinfo_or_arcname, bytes, permissions=0600, compression=ZIP_DEFLATED):
+    def writestr(self, zinfo_or_arcname, bytes, permissions=0600,
+            compression=ZIP_DEFLATED, raw_bytes=False):
         """Write a file into the archive.  The contents is the string
         'bytes'.  'zinfo_or_arcname' is either a ZipInfo instance or
         the name of the file in the archive."""
+        assert not raw_bytes or (raw_bytes and
+                isinstance(zinfo_or_arcname, ZipInfo))
         if not isinstance(zinfo_or_arcname, ZipInfo):
             if isinstance(zinfo_or_arcname, unicode):
                 zinfo_or_arcname = zinfo_or_arcname.encode('utf-8')
@@ -1177,18 +1200,20 @@ class ZipFile:
             raise RuntimeError(
                   "Attempt to write to ZIP archive that was already closed")
 
-        zinfo.file_size = len(bytes)            # Uncompressed size
+        if not raw_bytes:
+            zinfo.file_size = len(bytes)            # Uncompressed size
         zinfo.header_offset = self.fp.tell()    # Start of header bytes
         self._writecheck(zinfo)
         self._didModify = True
-        zinfo.CRC = crc32(bytes) & 0xffffffff       # CRC-32 checksum
-        if zinfo.compress_type == ZIP_DEFLATED:
-            co = zlib.compressobj(zlib.Z_DEFAULT_COMPRESSION,
-                 zlib.DEFLATED, -15)
-            bytes = co.compress(bytes) + co.flush()
-            zinfo.compress_size = len(bytes)    # Compressed size
-        else:
-            zinfo.compress_size = zinfo.file_size
+        if not raw_bytes:
+            zinfo.CRC = crc32(bytes) & 0xffffffff       # CRC-32 checksum
+            if zinfo.compress_type == ZIP_DEFLATED:
+                co = zlib.compressobj(zlib.Z_DEFAULT_COMPRESSION,
+                    zlib.DEFLATED, -15)
+                bytes = co.compress(bytes) + co.flush()
+                zinfo.compress_size = len(bytes)    # Compressed size
+            else:
+                zinfo.compress_size = zinfo.file_size
         zinfo.header_offset = self.fp.tell()    # Start of header bytes
         self.fp.write(zinfo.FileHeader())
         self.fp.write(bytes)
@@ -1332,7 +1357,7 @@ class ZipFile:
 def safe_replace(zipstream, name, datastream):
     '''
     Replace a file in a zip file in a safe manner. This proceeds by extracting
-    and re-creating the zipfile. This is neccessary because :method:`ZipFile.replace`
+    and re-creating the zipfile. This is necessary because :method:`ZipFile.replace`
     sometimes created corrupted zip files.
 
     :param zipstream:  Stream from a zip file
@@ -1340,21 +1365,20 @@ def safe_replace(zipstream, name, datastream):
     :param datastream: The data to replace the file with.
     '''
     z = ZipFile(zipstream, 'r')
-    names = z.infolist()
-    with TemporaryDirectory('_zipfile_replace') as tdir:
-        z.extractall(path=tdir)
-        mapping = z.extract_mapping
-        path = os.path.join(tdir, *name.split('/'))
-        shutil.copyfileobj(datastream, open(path, 'wb'))
+    with SpooledTemporaryFile(max_size=100*1024*1024) as temp:
+        ztemp = ZipFile(temp, 'w')
+        for obj in z.infolist():
+            if obj.filename == name:
+                ztemp.writestr(obj, datastream.read())
+            else:
+                ztemp.writestr(obj, z.read_raw(obj), raw_bytes=True)
+        ztemp.close()
+        z.close()
+        temp.seek(0)
         zipstream.seek(0)
         zipstream.truncate()
-        with closing(ZipFile(zipstream, 'w')) as z:
-            for info in names:
-                current = mapping[info.filename]
-                if os.path.isdir(current):
-                    z.writestr(info.filename+'/', '', 0700)
-                else:
-                    z.write(current, info.filename, compress_type=info.compress_type)
+        shutil.copyfileobj(temp, zipstream)
+        zipstream.flush()
 
 class PyZipFile(ZipFile):
     """Class to create ZIP archives with Python library files and packages."""