Instruction error with cache opcode

[John Miller <jamiller1110@cox.net>]

I am attempting to write a routine to initialize the cache for a MIPS
4kc core to get Linux 2.6.16.14 to compile.  I am sure someone has
probably already done this, but I am doing it for educational reasons. 
I am receiving the following error:

arch/mips/kernel/head.S: Assembler messages:
arch/mips/kernel/head.S:131: Error: Instruction cache requires absolute
expression

From the following code section:

	li	t0, 0x80000000  		# start address (KSEG0)
	addu	t1,t0,0x2000			# 8KB I-cache
1:	addu	t0,0x10				# 16B line size
	cache	Index_Store_Tag_I,-4(t0)	# clear tag
	nop
	cache	Fill_I,-4(t0)			# fill line
	nop
	bne	t0,t1,1b
	cache	Index_Store_Tag_I,-4(t0)

 I copied the code section from See MIPS Run, so I know the code must be
correct.  What am I doing wrong?