Something's wrong with the makefile indentation? (Makefile:x: *** missing separator. Stop.)

Question

I'm currently working on a research project, and we got to a point where we need to test execution times without cache memory enabled. I found a kernel module on https://www.linuxquestions.org/questions/linux-kernel-70/disabling-cpu-caches-936077/page2.html that enables and disables cache, but I just can't build it.

The makefile provided by "ulmo" is:

EXTRA_CFLAGS = -m32
obj-m += disableCache.o

all:
        make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

but everytime I run it, I get:

Makefile:5: *** missing separator.  Stop.

I have already tried to play with tabs and spaces (put 1 tab, 2 tabs, 4 spaces, 8 spaces, odd number of spaces), run the commands all alone in bash, and even replace $(shell uname -r) with my own linux version, but still get the same "syntax" error. I have little to no experience with Makefiles, so I really do not know why this is happening.