gzopen() and flock()

hi,

i've a problem with file locking.
seems that flock() and gzopen() do not work together. i get the error (or
warning) message ...

Warning: flock(): cannot represent a stream of type ZLIB as a File
Descriptor in ...

when using flock() after gzopen().

sourcecode looks like this ...

...
$entry_file = gzopen($entry_filename,'r');
// read content of entry_file (with read lock)
flock($entry_file, LOCK_SH);
....

i am using php 4.3.3 as apache modul on windows xp, on my webhosters
webserver php 4.2.3 on linux (where i've not tested yet).

does anyone has an idea what i am doing wrong or of an easy workaraound?

thx in advance
greetz
daniel