diff --git a/ChangeLog b/ChangeLog
index 0179c1985..10968929b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2008-05-29  Emmanuele Bassi  <ebassi@openedhand.com>
+
+	* configure.ac: Check the --with switches as soon as we have them,
+	to avoid further checks that will fail anyway.
+
 2008-05-29  Emmanuele Bassi  <ebassi@openedhand.com>
 
 	* README: Update the configure arguments list.
diff --git a/configure.ac b/configure.ac
index bbaa3d3d9..1190cde03 100644
--- a/configure.ac
+++ b/configure.ac
@@ -103,19 +103,28 @@ dnl ========================================================================
 
 backendextra=
 backendextralib=
-glesversion=1.1
 clutterbackend=glx
 AC_ARG_WITH([flavour],
-            AC_HELP_STRING([--with-flavour=@<:@glx/eglx/eglnative/sdl/osx@:>@],
+            AC_HELP_STRING([--with-flavour=@<:@glx/eglx/eglnative/sdl/osx/win32/fruity@:>@],
                            [Select the Clutter backend]),
             clutterbackend=$with_flavour)
 
+case $clutterbackend in
+  glx|eglx|eglnative|sdl|osx|win32|fruity) ;;
+  *) AC_MSG_ERROR([Invalid flavour $clutterbackend]) ;;
+esac
 
+glesversion=1.1
 AC_ARG_WITH([gles],
-            AC_HELP_STRING([--with-gles=@1.1/2.0@:>@],
+            AC_HELP_STRING([--with-gles=@<:@1.1/2.0@:>@],
                            [Select Clutter GLES version (for EGL backends)]),
             glesversion=$with_gles)
 
+case $glesversion in
+  1.1|2.0) ;;
+  *) AC_MSG_ERROR([Invalid GL ES version $glesversion])
+esac
+
 if test "x$clutterbackend" = "xfruity" 
 then
     if test "x$glesversion" != "x1.1"; then