diff --git a/x11-misc/xbatt/xbatt-1.3_rc1-r1.ebuild b/x11-misc/xbatt/xbatt-1.3_rc1-r1.ebuild
index 460d865a6a045..d9e0581b39b2c 100644
--- a/x11-misc/xbatt/xbatt-1.3_rc1-r1.ebuild
+++ b/x11-misc/xbatt/xbatt-1.3_rc1-r1.ebuild
@@ -3,7 +3,7 @@
 
 EAPI=8
 
-inherit toolchain-funcs
+inherit flag-o-matic toolchain-funcs
 
 MY_PV=${PV/_rc/pr}
 
@@ -36,6 +36,8 @@ PATCHES=(
 )
 
 src_configure() {
+	append-cflags -std=gnu89 # old codebase, incompatible with c2x
+
 	CC="$(tc-getBUILD_CC)" LD="$(tc-getLD)" \
 		IMAKECPP="${IMAKECPP:-${CHOST}-gcc -E}" xmkmf || die
 }