diff --git a/ai_edge_quantizer/model_modifier.py b/ai_edge_quantizer/model_modifier.py
index 434cc7b..07c8198 100644
--- a/ai_edge_quantizer/model_modifier.py
+++ b/ai_edge_quantizer/model_modifier.py
@@ -102,6 +102,13 @@ def _process_constant_map(
         buffer_size += len(buffer.data)
     return buffer_size
 
+  def _pad_bytearray(self, bytearr: bytearray):
+    """Pad the bytearray to 16 bytes."""
+    remainder = len(bytearr) % 16
+    if remainder != 0:
+      padding_size = 16 - remainder
+      bytearr.extend(b'\0' * padding_size)
+
   # TODO: b/333797307 - support > 2GB output model
   def _serialize_large_model(
       self, quantized_model: schema_py_generated.ModelT
@@ -123,12 +130,11 @@ def _serialize_large_model(
         buffer.data = None
         buffer.offset = 1
         buffer.size = 1
-    dummy_bytearray = flatbuffer_utils.convert_object_to_bytearray(
-        quantized_model
+    dummy_bytearray = bytearray(
+        flatbuffer_utils.convert_object_to_bytearray(quantized_model)
     )
     # calculate the correct buffer size and offset
-    while len(dummy_bytearray) % 16:
-      dummy_bytearray += b'\0'
+    self._pad_bytearray(dummy_bytearray)
     for buffer_idx, buffer in enumerate(quantized_model.buffers):
       buffer_data = self._constant_map[buffer_idx]
       if buffer_data is None:
@@ -136,23 +142,20 @@ def _serialize_large_model(
       buffer.offset = len(dummy_bytearray)
       buffer.size = len(buffer_data)
       dummy_bytearray += buffer_data
-      while len(dummy_bytearray) % 16:
-        dummy_bytearray += b'\0'
+      self._pad_bytearray(dummy_bytearray)
     del dummy_bytearray
 
     # build new tflite file with correct buffer offset
-    model_bytearray = flatbuffer_utils.convert_object_to_bytearray(
-        quantized_model
+    model_bytearray = bytearray(
+        flatbuffer_utils.convert_object_to_bytearray(quantized_model)
     )
-    while len(model_bytearray) % 16:
-      model_bytearray += b'\0'
+    self._pad_bytearray(model_bytearray)
     for buffer_idx, _ in enumerate(quantized_model.buffers):
       buffer_data = self._constant_map[buffer_idx]
       if buffer_data is None:
         continue
       model_bytearray += buffer_data
-      while len(model_bytearray) % 16:
-        model_bytearray += b'\0'
+      self._pad_bytearray(model_bytearray)
     return model_bytearray
 
   def _serialize_small_model(