diff --git a/debian/changelog b/debian/changelog
index 70092110..f07062b6 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -2,6 +2,9 @@ livecd-rootfs (2.466) UNRELEASED; urgency=medium
 
   * Factor out grub-related diversions and use them consistently, so we
     don't end up with wrong os-probe output in our grub.cfg.
+  * Fix the force-partuuid handling to create the file under
+    /etc/default/grub.d/ with a .cfg extension as grub expects; it's unclear
+    how this ever worked without.
 
  -- Steve Langasek <steve.langasek@ubuntu.com>  Wed, 04 Oct 2017 22:31:40 -0700
 
diff --git a/live-build/functions b/live-build/functions
index c421d2d7..4b316eb5 100644
--- a/live-build/functions
+++ b/live-build/functions
@@ -277,7 +277,7 @@ replace_grub_root_with_label() {
 
     # If boot by partuuid has been requested, don't override.
     if [ -f $CHROOT_ROOT/etc/default/grub.d/40-partuuid ] && \
-           grep -q ^GRUB_FORCE_PARTUUID= $CHROOT_ROOT/etc/default/grub.d/40-partuuid; then
+           grep -q ^GRUB_FORCE_PARTUUID= $CHROOT_ROOT/etc/default/grub.d/40-partuuid.cfg; then
         return 0
     fi
     sed -i -e "s,root=[^ ]\+,root=LABEL=${fs_label}," \
diff --git a/live-build/ubuntu-cpc/hooks/032-disk-image.binary b/live-build/ubuntu-cpc/hooks/032-disk-image.binary
index 006f289b..e369dfc9 100755
--- a/live-build/ubuntu-cpc/hooks/032-disk-image.binary
+++ b/live-build/ubuntu-cpc/hooks/032-disk-image.binary
@@ -124,7 +124,7 @@ if [ "${should_install_grub}" -eq 1 ]; then
 	if [ "${SUBPROJECT:-}" = minimized ] && [ -n "$partuuid" ]; then
 		echo "partuuid found for root device; forcing it in Grub"
 		mkdir -p mountpoint/etc/default/grub.d
-		echo "GRUB_FORCE_PARTUUID=$partuuid" >> mountpoint/etc/default/grub.d/40-force-partuuid
+		echo "GRUB_FORCE_PARTUUID=$partuuid" >> mountpoint/etc/default/grub.d/40-force-partuuid.cfg
 		divert_grub mountpoint
 		chroot mountpoint update-grub
 		undivert_grub mountpoint
diff --git a/live-build/ubuntu-cpc/hooks/033-disk-image-uefi.binary b/live-build/ubuntu-cpc/hooks/033-disk-image-uefi.binary
index 023228ae..8e8b0070 100755
--- a/live-build/ubuntu-cpc/hooks/033-disk-image-uefi.binary
+++ b/live-build/ubuntu-cpc/hooks/033-disk-image-uefi.binary
@@ -67,7 +67,7 @@ install_grub() {
         # and 033-disk-image-uefi.binary.  We want to fix this to not
         # have initramfs-tools installed at all on these images.
         echo "partuuid found for root device; omitting initrd"
-        echo "GRUB_FORCE_PARTUUID=$partuuid" >> mountpoint/etc/default/grub.d/40-force-partuuid
+        echo "GRUB_FORCE_PARTUUID=$partuuid" >> mountpoint/etc/default/grub.d/40-force-partuuid.cfg
     fi
 
     chroot mountpoint apt-get -y update