diff --git a/utils/AMS/hacking/mkamsboot.c b/utils/AMS/hacking/mkamsboot.c
index ea434bc893..f5c2f35d36 100644
--- a/utils/AMS/hacking/mkamsboot.c
+++ b/utils/AMS/hacking/mkamsboot.c
@@ -269,6 +269,7 @@ int main(int argc, char* argv[])
 
     put_uint32le(&buf[0x420], firmware_size + 1);  /* UCL unpack entry point */
     put_uint32le(&buf[0x424], firmware_size - ucl_size);  /* Location of OF */
+    put_uint32le(&buf[0x428], ucl_size);           /* Size of UCL image */
 
     /* Update checksum */
     sum = calc_checksum(buf + 0x400,firmware_size + uclunpack_size);
diff --git a/utils/AMS/hacking/test.S b/utils/AMS/hacking/test.S
index d4bb2143bb..2e1796fcef 100644
--- a/utils/AMS/hacking/test.S
+++ b/utils/AMS/hacking/test.S
@@ -18,6 +18,7 @@
 /* These values are filled in by mkamsboot - don't move them from offset 0x20 */
 ucl_unpack:      .word   0 /* Entry point (plus 1 - for thumb) of ucl_unpack */
 ucl_start:       .word   0 /* Start of the ucl-compressed OF image */
+ucl_size:        .word   0 /* Length in bytes of the compressed OF image */
 
 
 start:
@@ -29,6 +30,7 @@ loop:   subs  r1, r1, #1
         /* Call the ucl decompress function, which will branch to 0x0
            on completion */
         ldr   r0, ucl_start   /* Source */
-        mov   r1, #0          /* Destination */
-        ldr   r2, ucl_unpack
-        bx    r2
+        ldr   r1, ucl_size    /* Source length */
+        mov   r2, #0          /* Destination */
+        ldr   r3, ucl_unpack
+        bx    r3