Built header in different dir?

[Lars Hecking]

 How do I define a dependency on a header file in a different directory, eg.
 the parent dir? I tried

BUILT_SOURCES = ../header.h

 but automake tells me 

automake: subdir/Makefile.am: not supported: source file `../header.h' is in 
subdirectory

 This is automake 1.4 (and it must work with automake 1.4).

 Or is it just as simple as

file.o: ../header.h

 in subdir/Makefile.am?