--- configure.ac
+++ configure.ac
@@ -192,7 +192,10 @@
 dnl
 dnl check for Cg
 dnl
-if test "${have_fltk}" = yes; then
+AC_ARG_ENABLE(cg, AC_HELP_STRING([--enable-cg],
+  [enable nvidia cg support [[default=check]]]), [want_cg="${enableval}"], [want_cg=yes])
+
+if test "${have_fltk}" = yes -a "${want_cg}" != "no"; then
   AM_PATH_CG(have_cg=yes, have_cg=no)
   if test "${have_cg}" = yes; then
     AC_DEFINE(HAVE_FRAGMENT_SHADERS)