problem in gtk-xmhtml under solaris 2.5.1

[Federspiel <cfedersp debis com>]

Hello,
does anyone know how to fix the problem ?
Thanks

Making all in gtk-xmhtml
make[2]: Entering directory
`/var/src/gnome/gnome-libs-0.27.1/gtk-xmhtml'
/bin/sh ../libtool --mode=compile gcc -DHAVE_CONFIG_H -I. -I. -I.. -I..
-I./.. -I/usr/local/include -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/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-0.27.1/gtk-xmhtml'

make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/var/src/gnome/gnome-libs-0.27.1'
make: *** [all-recursive-am] Error 2
#