diff --git a/tools/rpi-otp-private-key b/tools/rpi-otp-private-key
index 68e8013..5d5a10f 100755
--- a/tools/rpi-otp-private-key
+++ b/tools/rpi-otp-private-key
@@ -50,8 +50,8 @@ check_key_set() {
 }
 
 read_key() {
-    out=READ_KEY="$(vcmailbox 0x00030081 $((8 + $ROW_COUNT * 4)) $((8 + $ROW_COUNT * 4)) $ROW_OFFSET $ROW_COUNT 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0)" || die "Failed to read the current key from OTP"
-    READ_KEY="$(echo "${out}" | sed 's/0x//g' | awk -v last=$((8 + $ROW_COUNT)) '{for(i=8;i<last;i++) printf $i; print ""}')"
+    out=READ_KEY="$(vcmailbox 0x00030081 $((8 + ROW_COUNT * 4)) $((8 + ROW_COUNT * 4)) $ROW_OFFSET $ROW_COUNT 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0)" || die "Failed to read the current key from OTP"
+    READ_KEY="$(echo "${out}" | sed 's/0x//g' | awk -v last=$((8 + ROW_COUNT)) '{for(i=8;i<last;i++) printf $i; print ""}')"
 }
 
 write_key() {
@@ -59,7 +59,7 @@ write_key() {
     # Normalize formatting and check the length
     key="$(echo "${key}" | tr 'A-Z' 'a-z')"
     key="$(echo "${key}" | sed 's/[^a-f0-9]//g')"
-    [ "$(echo -n "${key}" | wc -c)" = $(($ROW_COUNT * 4 * 2)) ] || die "Invalid key parameter"
+    [ "$(echo -n "${key}" | wc -c)" = $((ROW_COUNT * 4 * 2)) ] || die "Invalid key parameter"
 
     count=0
     key_params=""
@@ -83,7 +83,7 @@ write_key() {
        fi
     fi
 
-    vcmailbox 0x38081 $((8 + $ROW_COUNT * 4)) $((8 + $ROW_COUNT * 4)) $ROW_OFFSET $ROW_COUNT ${key_params} || die "Failed to write key"
+    vcmailbox 0x38081 $((8 + ROW_COUNT * 4)) $((8 + ROW_COUNT * 4)) $ROW_OFFSET $ROW_COUNT ${key_params} || die "Failed to write key"
     read_key
     [ "${READ_KEY}" = "${key}" ] || die "Key readback check failed. ${out}"
 }
@@ -151,7 +151,7 @@ fi
 if [ $ROW_OFFSET -lt 0 ]; then
     die "Offset too small"
 fi
-if [ ${ROW_OFFSET} -gt $(($MAX_ROW_COUNT - $ROW_COUNT)) ]; then
+if [ ${ROW_OFFSET} -gt $((MAX_ROW_COUNT - ROW_COUNT)) ]; then
     die "Offset too big"
 fi
 if [ -z $(which vcmailbox) ]; then