error in gtk-xmhtl or where to get xmp.h

[Federspiel <cfedersp debis com>]

Hello,
I've get an error during compilation, in the gtk-xmhtml dir,

# make

/bin/sh ../libtool --mode=compile gcc -DHAVE_CONFIG_H -I. -I. -I.. -I..
-I./.. -I/usr/local/include -I/usr/local/include
-I/usr/local/include/gtk -I/usr/openwin/include
-I/usr/local/lib/glib/include -I/usr/local/include -DWITH_GTK -DDEBUG
-DGNOME_LIB -I/usr/openwin/include -I/usr/local/lib/glib/include
-I/usr/local/include -g -O2 -c readXPM.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I./.. -I/usr/local/include
-I/usr/local/include -I/usr/local/include/gtk -I/usr/openwin/include
-I/usr/local/lib/glib/include -I/usr/local/include -DWITH_GTK -DDEBUG
-DGNOME_LIB -I/usr/openwin/include -I/usr/local/lib/glib/include
-I/usr/local/include -g -O2 -c -fPIC -DPIC readXPM.c
readXPM.c:136: X11/xpm.h: No such file or directory
make[2]: *** [readXPM.lo] Error 1
make[2]: Leaving directory '/var/src/gnome/gnome-libs-0.27/gtk-xmhtml'
make[1]: *** [all-recursice-am] Error 2
make[1]: Leaving directory '/var/src/gnome/gnome-libs-0.27/
make: *** [all-recursive-am] Error 2
#

Is the problem that xmp.h is missing, than please tell me where do I get
it, cause it's not on my disk.
Or let me know any other tips.
Thanks
Bye   Christian