Issue with simple Makefile: undefined reference to symbol 'cos@@GLIBC_2.2.5'

I'm trying to compìle some test C code using a Makefile. The `main.c` file includes two headers: ``` #include "circle_buffer.h" #include "window.h" ``` and when I execute the following Makefile ``` # compiler CC=gcc # compiler flags: # -g adds debugging information to the executable file # -Wall turns on most, but not all, compiler warnings CFLAGS= # include path INCLUDES = # library path and names LIBS=-L/usr/lib/x86_64-linux-gnu -lsndfile MAIN = test $(MAIN): main.o circle_buffer.o window.o $(CC) main.o circle_buffer.o window.o -o $(MAIN) $(LIBS) main.o: main.c circle_buffer.h window.h $(CC) -c main.c $(INCLUDES) circle_buffer.o: circle_buffer.c circle_buffer.h $(CC) -c circle_buffer.c $(INCLUDES) window.o: window.h $(CC) -c window.c $(INCLUDES) .PHONY: clean clean: rm -rf *o $(MAIN) ``` I get ``` xxx@xxx:~/source$ make gcc -c main.c gcc -c circle_buffer.c gcc -c window.c gcc main.o circle_buffer.o window.o -o test -L/usr/lib/x86_64-linux-gnu -lsndfile /usr/bin/ld: window.o: undefined reference to symbol 'cos@@GLIBC_2.2.5' //lib/x86_64-linux-gnu/libm.so.6: error adding symbols: DSO missing from command line collect2: error: ld returned 1 exit status make: *** [test] Error 1 ``` If I remove `#include "window.h"` from `main.c`, and all the references to window.o/h/c in the Makefile, it works. What am I missing? Where am I breaking the rule ``` target: dependencies [tab] system command ``` ?