diff --git a/sdk_container/src/third_party/portage-stable/eclass/optfeature.eclass b/sdk_container/src/third_party/portage-stable/eclass/optfeature.eclass
index f9870e0473..250a995901 100644
--- a/sdk_container/src/third_party/portage-stable/eclass/optfeature.eclass
+++ b/sdk_container/src/third_party/portage-stable/eclass/optfeature.eclass
@@ -1,14 +1,16 @@
 # Copyright 1999-2021 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
+# Flatcar: Support EAPI 0, 4 and 5.
+
 # @ECLASS: optfeature.eclass
 # @MAINTAINER:
 # base-system@gentoo.org
-# @SUPPORTED_EAPIS: 6 7 8
+# @SUPPORTED_EAPIS: 0 4 5 6 7 8
 # @BLURB: Advertise optional functionality that might be useful to users
 
-case ${EAPI} in
-	6|7|8) ;;
+case ${EAPI:-0} in
+	0|4|5|6|7|8) ;;
 	*) die "${ECLASS}: EAPI=${EAPI:-0} is not supported" ;;
 esac