How to compare two shell command output in Makefile?

My Makefile is:

.PHONY: check
check:
        ifneq $(shell echo 123), $(shell echo 123)
                $(error Not equal)
        endif

When I run, I've got the error:

$ make
Makefile:3: *** Not equal.  Stop.

But this should happen only when they're different, but they're not. Why?