dropbear compile error

Does any one get this error on compiling when enabling dropbear???

configure: error: *** zlib missing - install first or check config.log ***

I downloaded the nios2-linux-20090929.tar (linux-mmu) and did

./checkout and ./update

Then menuconfig and enabled dropbear.

Since I did not change H/W setting, I assume it is the default custom_fpga setting.