diff --git a/npk.py b/npk.py
index 5a21172..685efa3 100644
--- a/npk.py
+++ b/npk.py
@@ -207,10 +207,9 @@ class NovaPackage(Package):
                     self._parts.append(NpkPartItem(NpkPartID(part_id),NpkInfo.unserialize_from(part_data)))
                 else:
                     self._parts.append(NpkPartItem(NpkPartID(part_id),part_data))
+
     def set_null_block(self):
         def rebuild_squashfs(data):
-            if len(part.data) < 4 or part.data[:4] != b'hsqs':
-                return part.data
             with open('squashfs.sfs', 'wb') as f:
                 f.write(data)
             os.system('unsquashfs -d squashfs-root squashfs.sfs')
@@ -219,19 +218,20 @@ class NovaPackage(Package):
             os.system('rm -rf squashfs-root')
             with open('squashfs.sfs', 'rb') as f:
                 return f.read()
-
-        if len(self._packages) > 0:
+        def get_size(package,size=8):
+            for part in package._parts:
+                size += 6
+                size += len(part.data)
+            return size
+           
+        def set_null(package,offset=None):
             has_squashfs = False
-            for package in self._packages:
-                for part in package._parts:
-                    if part.id == NpkPartID.SQUASHFS:
-                        part.data = rebuild_squashfs(part.data)
-                        has_squashfs = True
-
-            if not has_squashfs:
-                return
-            for package in self._packages:
-                count = 8
+            for part in package._parts:
+                if part.id == NpkPartID.SQUASHFS and len(part.data) >= 4 and  part.data[:4] in [b'hsqs',b'sqsh']:
+                    part.data = rebuild_squashfs(part.data)
+                    has_squashfs = True
+            if has_squashfs:
+                count = offset or 8
                 for part in package._parts:
                     count += 6
                     if part.id == NpkPartID.NULL_BLOCK:
@@ -241,23 +241,12 @@ class NovaPackage(Package):
                 pad_len = (4096 - (count % 4096)) % 4096
                 package[NpkPartID.NULL_BLOCK].data = b'\x00' * pad_len
 
-        else:
-            has_squashfs = False
-            for part in self._parts:
-                if part.id == NpkPartID.SQUASHFS:
-                    part.data = rebuild_squashfs(part.data)
-                    has_squashfs = True
-            if not has_squashfs:
-                return
-            count = 8
-            for part in self._parts:
-                count += 6
-                if part.id == NpkPartID.NULL_BLOCK:
-                    break
-                count += len(part.data)
-            count += 6
-            pad_len = (4096 - (count % 4096)) % 4096
-            self[NpkPartID.NULL_BLOCK].data = b'\x00' * pad_len
+        set_null(self)
+        offset = get_size(self)
+        for package in self._packages:
+            set_null(package,offset)
+            offset += get_size(package,0)
+            
     def get_digest(self,hash_fnc,package:Package=None)->bytes:
         parts = package._parts if package else self._parts
         for part in parts: