Index: pyyaml/trunk/setup.py
===================================================================
--- pyyaml/trunk/setup.py	(revision 322)
+++ pyyaml/trunk/setup.py	(revision 325)
@@ -221,5 +221,6 @@
                     depends=ext.depends)
         except CompileError:
-            log.warn("%s appears not to be installed" % ext.feature_name)
+            log.warn("%s appears not to be installed: forcing --%s"
+                     % (ext.feature_name, ext.neg_option_name))
             log.warn("(if %s is installed, you may need to specify"
                     % ext.feature_name)