diff --git a/gp2040ce_bintools/builder.py b/gp2040ce_bintools/builder.py
index 540381b..32a8b6a 100644
--- a/gp2040ce_bintools/builder.py
+++ b/gp2040ce_bintools/builder.py
@@ -95,15 +95,25 @@ def concatenate_firmware_and_storage_files(firmware_filename: str,
             user_config_binary = serialize_config_with_footer(config)
 
     with open(firmware_filename, 'rb') as firmware:
-        new_binary = combine_firmware_and_config(bytearray(firmware.read()), board_config_binary, user_config_binary,
+        firmware_binary = bytearray(firmware.read())
+
+    # create a sequential binary for .bin and USB uses, or index it for .uf2
+    if usb or combined_filename[-4:] != '.uf2':
+        new_binary = combine_firmware_and_config(firmware_binary, board_config_binary, user_config_binary,
                                                  replace_extra=replace_extra)
+    else:
+        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)
 
     if combined_filename:
         with open(combined_filename, 'wb') as combined:
-            if combined_filename[-4:] == '.uf2':
-                combined.write(convert_binary_to_uf2(new_binary))
-            else:
-                combined.write(new_binary)
+            combined.write(new_binary)
+
     if usb:
         endpoint_out, endpoint_in = get_bootsel_endpoints()
         write(endpoint_out, endpoint_in, GP2040CE_START_ADDRESS, bytes(new_binary))
diff --git a/tests/test_builder.py b/tests/test_builder.py
index e73ff1e..b61c651 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
@@ -110,6 +111,33 @@ def test_concatenate_to_usb(tmp_path):
     assert len(mock_write.call_args.args[3]) == 2 * 1024 * 1024
 
 
+def test_concatenate_to_uf2(tmp_path, firmware_binary, config_binary):
+    """Test that we write a UF2 file as expected."""
+    tmp_file = os.path.join(tmp_path, 'concat.uf2')
+    firmware_file = os.path.join(HERE, 'test-files', 'test-firmware.bin')
+    config_file = os.path.join(HERE, 'test-files', 'test-config.bin')
+    concatenate_firmware_and_storage_files(firmware_file, binary_board_config_filename=config_file,
+                                           binary_user_config_filename=config_file,
+                                           combined_filename=tmp_file)
+    with open(tmp_file, 'rb') as file:
+        content = file.read()
+    # size of the file should be 2x firmware in 256 byte blocks + 2x padded board config + 2x padding user config
+    assert len(content) == 2 * (math.ceil(len(firmware_binary)/256) * 256) + 2 * STORAGE_SIZE + 2 * STORAGE_SIZE
+
+
+def test_concatenate_to_uf2_board_only(tmp_path, firmware_binary, config_binary):
+    """Test that we write a UF2 file as expected."""
+    tmp_file = os.path.join(tmp_path, 'concat.uf2')
+    firmware_file = os.path.join(HERE, 'test-files', 'test-firmware.bin')
+    config_file = os.path.join(HERE, 'test-files', 'test-config.bin')
+    concatenate_firmware_and_storage_files(firmware_file, binary_board_config_filename=config_file,
+                                           combined_filename=tmp_file)
+    with open(tmp_file, 'rb') as file:
+        content = file.read()
+    # size of the file should be 2x firmware in 256 byte blocks + 2x padded board config + 2x padding user config
+    assert len(content) == 2 * (math.ceil(len(firmware_binary)/256) * 256) + 2 * STORAGE_SIZE
+
+
 def test_padding_firmware(firmware_binary):
     """Test that firmware is padded to the expected size."""
     padded = pad_binary_up_to_user_config(firmware_binary)
diff --git a/tests/test_storage.py b/tests/test_storage.py
index cb12e75..5ef8da3 100644
--- a/tests/test_storage.py
+++ b/tests/test_storage.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
@@ -139,6 +140,15 @@ def test_convert_binary_to_uf2(whole_board_with_board_config_dump):
     assert uf2[524:528] == bytearray(b'\x00\x01\x00\x10')   # address to write the second chunk
 
 
+def test_convert_unaligned_binary_to_uf2(firmware_binary):
+    """Do some sanity checks in the attempt to convert a binary to a UF2."""
+    uf2 = storage.convert_binary_to_uf2(firmware_binary)
+    assert len(uf2) == math.ceil(len(firmware_binary)/256) * 512    # 256 byte complete/partial chunks -> 512 b chunks
+    assert uf2[0:4] == b'\x55\x46\x32\x0a' == b'UF2\n'      # proper magic
+    assert uf2[8:12] == bytearray(b'\x00\x20\x00\x00')      # family ID set
+    assert uf2[524:528] == bytearray(b'\x00\x01\x00\x10')   # address to write the second chunk
+
+
 def test_convert_binary_to_uf2_with_offsets(whole_board_with_board_config_dump):
     """Do some sanity checks in the attempt to convert a binary to a UF2."""
     uf2 = storage.convert_binary_to_uf2(whole_board_with_board_config_dump, start=storage.USER_CONFIG_BINARY_LOCATION)