No rule to make target 'bzr.mk', needed by 'all-am'

[Sascha Manns]

Hello list,

i have a project what provides a file called "bzr.mk". This isnt
generated and should just installed in $(datadir)/bzrmk.

For doing that i have a src/Makefile.am:
bzrmkdir = $(datadir)/bzrmk/
# Not generated
bzrmk_DATA = bzr.mk

But while building the package i'm getting:
Making all in src
make[3]: Entering directory '/build/bzrmk-1.2.1/src'
make[3]: *** No rule to make target 'bzr.mk', needed by 'all-
am'.  Stop.
make[3]: Leaving directory '/build/bzrmk-1.2.1/src'
Makefile:464: recipe for target 'all-recursive' failed

Full project's url: https://bazaar.launchpad.net/~sascha-manns-h/bzrmk/
trunk/files

Maybe anyone knows why make searches for a bzr.mk rule?

Greetings
Sascha