While doing bug 436260 I noticed this in configure.ac: dnl XF86VidMode HAVE_XF86VMODE=no XF86VMODE_LIB= CPPFLAGS_SAVE=$CPPFLAGS CPPFLAGS="$CPPFLAGS $X_CFLAGS" AC_CHECK_HEADERS([X11/extensions/xf86vmode.h], [AC_CHECK_LIB([Xxf86vm], [XF86VidModeSwitchToMode], [AC_DEFINE([HAVE_XF86VMODE], [], [XF86VidMode is available]) XF86VMODE_LIB=-lXxf86vm HAVE_XF86VMODE=yes], [], [$X_LIBS])], [], [#include <X11/Xlib.h> ] ) CPPFLAGS=$CPPFLAGS_SAVE AC_SUBST([XF86VMODE_LIB]) AM_CONDITIONAL([HAVE_XF86VMODE], [test "$HAVE_XF86VMODE" = "yes"]) If xf86vidmode is detected, it looks like it tries to build against it... but I can't find any uses of HAVE_XF86VMODE or XF86VMODE_LIB in the Makefiles. Could someone double check me that it's not actually using xf86vidmode?