--- Lib/zipfile.py
+++ Lib/zipfile.py
@@ -554,7 +554,7 @@ class ZipFile:
         else:
             zinfo.compress_type = compress_type
 
-        zinfo.file_size = st.st_size
+        zinfo.file_size = file_size = st.st_size
         zinfo.flag_bits = 0x00
         zinfo.header_offset = self.fp.tell()    # Start of header bytes
 
@@ -564,13 +564,13 @@ class ZipFile:
         # Must overwrite CRC and sizes with correct data later
         zinfo.CRC = CRC = 0
         zinfo.compress_size = compress_size = 0
-        zinfo.file_size = file_size = 0
         self.fp.write(zinfo.FileHeader())
         if zinfo.compress_type == ZIP_DEFLATED:
             cmpr = zlib.compressobj(zlib.Z_DEFAULT_COMPRESSION,
                  zlib.DEFLATED, -15)
         else:
             cmpr = None
+        file_size = 0
         while 1:
             buf = fp.read(1024 * 8)
             if not buf:
@@ -593,9 +593,8 @@ class ZipFile:
         zinfo.file_size = file_size
         # Seek backwards and write CRC and file sizes
         position = self.fp.tell()       # Preserve current position in file
-        self.fp.seek(zinfo.header_offset + 14, 0)
-        self.fp.write(struct.pack("<lLL", zinfo.CRC, zinfo.compress_size,
-              zinfo.file_size))
+        self.fp.seek(zinfo.header_offset, 0)
+        self.fp.write(zinfo.FileHeader())
         self.fp.seek(position, 0)
         self.filelist.append(zinfo)
         self.NameToInfo[zinfo.filename] = zinfo