Different behavior of mktemp Ubuntu 12.02 / Mint 9 Isadora

Different behavior of mktemp Ubuntu 12.02 / Mint 9 Isadora

In a bash script I use ImageMagick's convert command for doing some image
processing.
I generate a temporal gif file for convert to write to.
I really need the file to have the .gif extension so convert knows that
the destination file should be a gif file.
In Ubuntu 12.04 the following works fine:
mktemp /tmp/pre_XXXXXXXXXX.gif
But in Mint 9 Isadora I get the following error:
mktemp: too few X's in template
No matter how many X's I give it, it gives the same error, which is only
fixed when I delete the ".gif" suffix.
Why is that ? Isn't Mint based on Ubuntu ?