diff --git a/sdk_container/src/third_party/coreos-overlay/coreos/config/env/sys-boot/grub b/sdk_container/src/third_party/coreos-overlay/coreos/config/env/sys-boot/grub
index ed33d6062d..223641d3e1 100644
--- a/sdk_container/src/third_party/coreos-overlay/coreos/config/env/sys-boot/grub
+++ b/sdk_container/src/third_party/coreos-overlay/coreos/config/env/sys-boot/grub
@@ -1,10 +1,20 @@
+# Bump the flatcar version stated here every time we or Gentoo change patches
+# that modify parts of GRUB that are installed to the boot partition. Reset the
+# version back to 1 when the upstream GRUB version changes.
+FLATCAR_VERSION=flatcar1
+
+# Adjust the version string for Flatcar. This propagates throughout the source.
+cros_pre_src_prepare_adjust_version() {
+	sed -i "/AC_INIT/s/\b${PV//./\\.}\b/\0-${FLATCAR_VERSION}/g" configure.ac || die
+}
+
 # Replace Gentoo's SBAT with Flatcar's.
 cros_post_src_install_sbat() {
 	insinto /usr/share/grub
 	newins - sbat.csv <<-EOF
 		sbat,1,SBAT Version,sbat,1,https://github.com/rhboot/shim/blob/main/SBAT.md
 		grub,4,Free Software Foundation,grub,${PV},https://www.gnu.org/software/grub/
-		grub.flatcar,1,Flatcar,grub2,${PVR},https://github.com/flatcar/Flatcar
+		grub.flatcar,1,Flatcar,grub2,${PV}-${FLATCAR_VERSION},https://github.com/flatcar/Flatcar
 	EOF
 }