diff --git a/config.usage b/config.usage
index dc892e7..f384ffe 100644
--- a/config.usage
+++ b/config.usage
@@ -125,6 +125,8 @@ supported variables:
 	CFLAGS_CMDLINE
 	CFLAGS_CONFIG
 	CFLAGS_SYSROOT
+	CFLAGS_OS
+	CFLAGS_SITE
 	CFLAGS_PATH
 	CFLAGS_STRICT
 	CFLAGS_UTIL