diff --git a/debian/changelog b/debian/changelog
index ebc2f625..11b79973 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,10 @@
+debian-cd (3.1.19) UNRELEASED; urgency=medium
+
+  [ Steve McIntyre ]
+  * Also fix size calculation for EFI image for arm64
+
+ -- Steve McIntyre <93sam@debian.org>  Fri, 06 May 2016 22:59:32 +0100
+
 debian-cd (3.1.18) unstable; urgency=medium
 
   [ Steve McIntyre ]
diff --git a/tools/boot/stretch/boot-arm64 b/tools/boot/stretch/boot-arm64
index fd736abf..ac36c8b0 100755
--- a/tools/boot/stretch/boot-arm64
+++ b/tools/boot/stretch/boot-arm64
@@ -93,12 +93,39 @@ if [ -d boot$N/grub ] ; then
     # This is the same as in efi-image, but we need to redo it here in
     # the case of a multi-arch image
 
-    size=0
-    for file in $CDDIR/efi/boot/boot*.efi; do
-        size=$(($size + $(stat -c %s "$file")))
-    done
+    # Stuff the EFI boot files into a FAT filesystem, making it as
+    # small as possible.
 
-    blocks=$((($size / 1024 + 55) / 32 * 32 ))
+    sector_bytes=512 # -S
+    cluster_sectors=4 # -s
+    cluster_bytes=$((sector_bytes * cluster_sectors))
+
+    clusters=2 # 1 cluster for each sub-directory
+    for file in $CDDIR/efi/boot/boot*.efi; do
+        [ -f "$file" ] || continue
+        clusters=$(($clusters + (($(stat -c %s "$file") + $cluster_bytes - 1) / $cluster_bytes)))
+    done
+    reserved_sectors=1 # boot-sector -R
+    reserved_bytes=$(($reserved_sectors * $sector_bytes))
+    fat_copies=2 # -f
+    if [ "$clusters" -le $(((1 << 12) - 2)) ]; then
+        fat_entry_bytes=3/2 # -F
+    elif [ "$clusters" -le $(((1 << 16) - 2)) ]; then
+        fat_entry_bytes=2 # -F
+    else
+        fat_entry_bytes=4 # -F
+    fi
+    fat_bytes=$((($clusters * $fat_entry_bytes + $sector_bytes - 1) / $sector_bytes * $sector_bytes))
+    root_entries=512 # -r
+    root_entry_bytes=32
+    root_bytes=$(($root_entries * root_entry_bytes))
+    size=$(($reserved_bytes + $fat_copies * $fat_bytes + $root_bytes + $clusters * $cluster_bytes))
+
+    track_sectors=32
+    track_bytes=$((sector_bytes * $track_sectors))
+    tracks=$((($size + $track_bytes - 1) / $track_bytes))
+    block_bytes=1024
+    blocks=$(($tracks * $track_bytes / $block_bytes))
 
     rm -f $CDDIR/boot/grub/efi.img
     mkfs.msdos -C "$CDDIR/boot/grub/efi.img" $blocks >/dev/null