diff --git a/common/mkfirmware.sh b/common/mkfirmware.sh
index 9cde466..7f5113d 100755
--- a/common/mkfirmware.sh
+++ b/common/mkfirmware.sh
@@ -85,7 +85,7 @@ assert_size() {
 
     IMG_SIZE=$(stat -c "%s" "$IMG")
 
-    if [ $PART_SIZE -lt $(( "$IMG_SIZE" / 1024 )) ]; then
+    if [ $PART_SIZE -lt $(( $IMG_SIZE / 1024 )) ]; then
         fatal "error: $IMG's size exceed parameter.txt's limit!"
     fi
 }