diff --git a/x11-terms/kitty/kitty-9999.ebuild b/x11-terms/kitty/kitty-9999.ebuild
index 4c3dc7d623f01..66daa0ec2a6da 100644
--- a/x11-terms/kitty/kitty-9999.ebuild
+++ b/x11-terms/kitty/kitty-9999.ebuild
@@ -103,6 +103,7 @@ src_prepare() {
 	local sedargs=(
 		-e "/num_workers =/s/=.*/= $(makeopts_jobs)/"
 		-e "s/cflags.append.*-O3.*/pass/" -e 's/-O3//'
+		-e "s/cflags.append(fortify_source)/pass/" # use toolchain's _f_s
 		-e "s/ld_flags.append('-[sw]')/pass/"
 	)