diff --git a/meta-refkit/classes/image-dsk.bbclass b/meta-refkit/classes/image-dsk.bbclass
index f3b7b8397f..d1366a5769 100644
--- a/meta-refkit/classes/image-dsk.bbclass
+++ b/meta-refkit/classes/image-dsk.bbclass
@@ -75,7 +75,7 @@ DSK_IMAGE_LAYOUT ??= ' \
     "partition_01_primary_uefi_boot": { \
         "name": "primary_uefi", \
         "uuid": 0, \
-        "size_mb": 15, \
+        "size_mb": ${REFKIT_VFAT_MB}, \
         "source": "${IMAGE_ROOTFS}/boot/", \
         "filesystem": "vfat", \
         "type": "${PARTITION_TYPE_EFI}" \
@@ -83,7 +83,7 @@ DSK_IMAGE_LAYOUT ??= ' \
     "partition_02_secondary_uefi_boot": { \
         "name": "secondary_uefi", \
         "uuid": 0, \
-        "size_mb": 15, \
+        "size_mb": ${REFKIT_VFAT_MB}, \
         "source": "${IMAGE_ROOTFS}/boot/", \
         "filesystem": "vfat", \
         "type": "${PARTITION_TYPE_EFI_BACKUP}" \
diff --git a/meta-refkit/classes/refkit-image.bbclass b/meta-refkit/classes/refkit-image.bbclass
index 78be54db69..a697e3249a 100644
--- a/meta-refkit/classes/refkit-image.bbclass
+++ b/meta-refkit/classes/refkit-image.bbclass
@@ -274,7 +274,13 @@ IMAGE_FSTYPES_remove = "live"
 # Activate "dsk" image type.
 IMAGE_CLASSES += "${@ 'image-dsk' if ${REFKIT_USE_DSK_IMAGES} else ''}"
 
+# By default, the full image is meant to fit into 4*10^9 bytes, i.e.
+# "4GB" regardless whether 1000 or 1024 is used as base. 64M are reserved
+# for potential partitioning overhead.
 WKS_FILE = "refkit-directdisk.wks.in"
+REFKIT_VFAT_MB ??= "64"
+REFKIT_IMAGE_SIZE ??= "--fixed-size 3622M"
+REFKIT_EXTRA_PARTITION ??= ""
 WIC_CREATE_EXTRA_ARGS += " -D"
 
 # Inherit after setting variables that get evaluated when importing
diff --git a/meta-refkit/wic/refkit-directdisk.wks.in b/meta-refkit/wic/refkit-directdisk.wks.in
index a3cc14324a..7bc7eddb8a 100644
--- a/meta-refkit/wic/refkit-directdisk.wks.in
+++ b/meta-refkit/wic/refkit-directdisk.wks.in
@@ -4,6 +4,6 @@
 # EFI stub, kernel, kernel cmdline, and the initrd
 
 bootloader --ptable gpt
-part --source rootfs --rootfs-dir=${IMAGE_ROOTFS}/boot --fstype=vfat --fixed-size 30M --label primary_uefi --part-type C12A7328-F81F-11D2-BA4B-00A0C93EC93B --align 1024 --use-uuid
-part --source rootfs --rootfs-dir=${IMAGE_ROOTFS}/boot --fstype=vfat --fixed-size 30M --label secondary_uefi --part-type E3C9E316-0B5C-4DB8-817D-F92DF00215AE --align 1024 --use-uuid
-part / --source rootfs --fixed-size 3700M --fstype=ext4 --label rootfs --align 1024 --uuid ${REMOVABLE_MEDIA_ROOTFS_PARTUUID_VALUE}
+part --source rootfs --rootfs-dir=${IMAGE_ROOTFS}/boot --fstype=vfat --fixed-size ${REFKIT_VFAT_MB}M --label primary_uefi --part-type C12A7328-F81F-11D2-BA4B-00A0C93EC93B --align 1024 --use-uuid
+part --source rootfs --rootfs-dir=${IMAGE_ROOTFS}/boot --fstype=vfat --fixed-size ${REFKIT_VFAT_MB}M --label secondary_uefi --part-type E3C9E316-0B5C-4DB8-817D-F92DF00215AF --align 1024 --use-uuid
+part / --source rootfs ${REFKIT_IMAGE_SIZE} --fstype=ext4 --label rootfs --align 1024 --uuid ${REMOVABLE_MEDIA_ROOTFS_PARTUUID_VALUE}