diff --git a/mkapp/app/script/formatsd.sh b/mkapp/app/script/formatsd.sh
index 4b3f543db..8d6464711 100755
--- a/mkapp/app/script/formatsd.sh
+++ b/mkapp/app/script/formatsd.sh
@@ -17,9 +17,10 @@ else
     echo "Umounting SD Card: FAILURE"
 fi
 
-BLKDEV=/dev/mmcblk0p1
+DISKDEV=/dev/mmcblk0
+BLKDEV=${DISKDEV}p1
 if [ ! -b "$BLKDEV" ]; then
-    BLKDEV=/dev/mmcblk0
+    BLKDEV=$DISKDEV
 fi
 
 rm -f /tmp/mkfs.result
@@ -28,6 +29,25 @@ RESULT=$?
 echo "mkfs result: $RESULT" >> /tmp/mkfs.log
 echo $RESULT > /tmp/mkfs.result
 
+# mkfs.vfat only rewrites the filesystem inside the partition; the MBR
+# partition type byte is left as it was. SDXC cards (>32GB) ship as exFAT
+# with type 0x07 (NTFS/exFAT), so after formatting they hold FAT32 in a
+# partition still labelled 0x07. Linux ignores the type byte and mounts
+# fine, but macOS picks the filesystem driver from it, tries exFAT, and
+# reports "The disk you attached was not readable by this computer".
+# Set the type to 0x0C (FAT32 LBA) so the card mounts on every OS.
+# Only the 0x07 case is touched; 0xEE (GPT protective MBR) and anything
+# already FAT-typed are left alone.
+if [ "$RESULT" -eq 0 ] && [ "$BLKDEV" != "$DISKDEV" ]; then
+    PTYPE=$(dd if="$DISKDEV" bs=1 skip=450 count=1 2>/dev/null | hexdump -v -e '1/1 "%02x"')
+    echo "partition type: 0x$PTYPE" >> /tmp/mkfs.log
+    if [ "$PTYPE" = "07" ]; then
+        printf '\014' | dd of="$DISKDEV" bs=1 seek=450 count=1 conv=notrunc,fsync >> /tmp/mkfs.log 2>&1
+        blockdev --rereadpt "$DISKDEV" >> /tmp/mkfs.log 2>&1
+        echo "partition type changed to 0x0c (FAT32 LBA)" >> /tmp/mkfs.log
+    fi
+fi
+
 echo "Mounting SD Card"
 mount "$BLKDEV" /mnt/extsd
 if [ $? -eq 0 ]; then