--- configure.ac
+++ configure.ac
@@ -187,7 +187,12 @@
 dnl
 dnl check for Cg
 dnl
-if test "${have_fltk}" = yes; then
+AC_ARG_ENABLE(nvidia,
+              AC_HELP_STRING([--enable-nvidia],
+                             [enable NVIDIA Cg support [[default=check]]]),
+              [want_nvidia="${enableval}"], [want_nvidia=yes])
+
+if test "${have_fltk}" = yes -a "${want_nvidia}" != "no"; then
   AM_PATH_CG(have_cg=yes, have_cg=no)
   if test "${have_cg}" = yes; then
     AC_DEFINE(HAVE_FRAGMENT_SHADERS)