'.' is not a valid target

In my makefiles, I try to make sure that output directories always exist before they are used. In the default case, the output directory is simply '.'. So you get:
X = .
$(X):
@if not exist $(X) @echo mkdir $(X) & @mkdir $(X)

all: $(X)

jom flags the second line as a syntax error. Nmake does accept '.' as a valid target.