diff --git a/gp2040ce_bintools/builder.py b/gp2040ce_bintools/builder.py
index 502545c..1ae45b0 100644
--- a/gp2040ce_bintools/builder.py
+++ b/gp2040ce_bintools/builder.py
@@ -101,26 +101,15 @@ def concatenate_firmware_and_storage_files(firmware_filename: str,
         new_binary = combine_firmware_and_config(firmware_binary, board_config_binary, user_config_binary,
                                                  replace_extra=replace_extra)
     else:
-        # this was kind of fine, but combining multiple calls of convert_binary_to_uf2 produced
-        # incorrect total block counts in the file, which picotool handled with some squirrely
-        # double-output behavior that has me worried it'd cause a real issue, so doing the
-        # crude padding + write of empty blocks, for now...
-        #
-        # new_binary = convert_binary_to_uf2(firmware_binary)
-        # if board_config_binary:
-        #     new_binary += convert_binary_to_uf2(pad_config_to_storage_size(board_config_binary),
-        #                                         start=BOARD_CONFIG_BINARY_LOCATION)
-        # if user_config_binary:
-        #     new_binary += convert_binary_to_uf2(pad_config_to_storage_size(user_config_binary),
-        #                                         start=USER_CONFIG_BINARY_LOCATION)
-        #
-        # the correct way to do the above would be to pass a list of {offset,binary_data} to convert...,
-        # and have it calculate the total block size before starting to write, and then iterating over
-        # the three lists. doable, just not on the top of my mind right now
-        new_binary = storage.convert_binary_to_uf2([
-            (0, combine_firmware_and_config(firmware_binary, board_config_binary, user_config_binary,
-                                            replace_extra=replace_extra)),
-        ])
+        binary_list = [(0, firmware_binary)]
+        # we must pad to storage start in order for the UF2 write addresses to make sense
+        if board_config_binary:
+            binary_list.append((storage.BOARD_CONFIG_BINARY_LOCATION,
+                                storage.pad_config_to_storage_size(board_config_binary)))
+        if user_config_binary:
+            binary_list.append((storage.USER_CONFIG_BINARY_LOCATION,
+                                storage.pad_config_to_storage_size(user_config_binary)))
+        new_binary = storage.convert_binary_to_uf2(binary_list)
 
     if combined_filename:
         with open(combined_filename, 'wb') as combined:
@@ -257,6 +246,7 @@ def write_new_config_to_filename(config: Message, filename: str, inject: bool =
         binary = storage.serialize_config_with_footer(config)
         with open(filename, 'wb') as file:
             if filename[-4:] == '.uf2':
+                # we must pad to storage start in order for the UF2 write addresses to make sense
                 file.write(storage.convert_binary_to_uf2([
                     (storage.USER_CONFIG_BINARY_LOCATION, storage.pad_config_to_storage_size(binary)),
                 ]))
diff --git a/tests/test_builder.py b/tests/test_builder.py
index 09c4f48..d55d100 100644
--- a/tests/test_builder.py
+++ b/tests/test_builder.py
@@ -3,6 +3,7 @@
 SPDX-FileCopyrightText: © 2023 Brian S. Stephan <bss@incorporeal.org>
 SPDX-License-Identifier: GPL-3.0-or-later
 """
+import math
 import os
 import sys
 import unittest.mock as mock
@@ -117,8 +118,9 @@ def test_concatenate_to_uf2(tmp_path, firmware_binary, config_binary):
                                                    combined_filename=tmp_file)
     with open(tmp_file, 'rb') as file:
         content = file.read()
-    # size of the file should be 2x the binary version, and the binary is 2 MB
-    assert len(content) == 2 * 2 * 1024 * 1024
+    # size of the file should be 2x the padded firmware + 2x the board config space + 2x the user config space
+    assert len(content) == (math.ceil(len(firmware_binary)/256) * 512 +
+                            math.ceil(STORAGE_SIZE/256) * 512 * 2)
 
 
 def test_concatenate_to_uf2_board_only(tmp_path, firmware_binary, config_binary):
@@ -130,8 +132,9 @@ def test_concatenate_to_uf2_board_only(tmp_path, firmware_binary, config_binary)
                                                    combined_filename=tmp_file)
     with open(tmp_file, 'rb') as file:
         content = file.read()
-    # size of the file should be 2x the binary version (minus user config space), and the binary is 2 MB - 16KB
-    assert len(content) == 2 * (2 * 1024 * 1024 - 16384)
+    # size of the file should be 2x the padded firmware + 2x the board config space
+    assert len(content) == (math.ceil(len(firmware_binary)/256) * 512 +
+                            math.ceil(STORAGE_SIZE/256) * 512)
 
 
 def test_find_version_string(firmware_binary):