UART Buffer Length Issue

I am trying to change the UART buffer length from 64 bytes to a larger value to facilitate a message being received that is greater than 64 bytes. I cannot control the size of the message that is being sent to my system, so this is critical that I am able to change the size of the buffer. I located the# define in the altera_avalon_uart.h that defines the buffer size and I changed it to the desired length. Upon doing this, when messages were not being transmitted, my system entered the alt_irq_entry() function and never returned. If anyone knows what is going on here please help. Thanks!