Adler32 Python DeprecationWarning

[jspiro]

Line 91: newextra = struct.pack("<2HI",0xdada,0x0004,adler32)

results in

sys:1: DeprecationWarning: struct integer overflow masking is deprecated
sys:1: DeprecationWarning: 'I' format requires 0 <= number <= 4294967295

on OS X 10.6 with Python 2.6 and a zip file created with MacPorts zip.

Changing the format to use a lowercase i from I makes the error go away, as adler32 returns signed integers. Is that a safe change?