diff --git a/gp2040ce_bintools/builder.py b/gp2040ce_bintools/builder.py
index 32a8b6a..cfc203b 100644
--- a/gp2040ce_bintools/builder.py
+++ b/gp2040ce_bintools/builder.py
@@ -102,13 +102,24 @@ 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:
-        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)
+        # 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 = convert_binary_to_uf2(combine_firmware_and_config(firmware_binary, board_config_binary,
+                                                                       user_config_binary, replace_extra=replace_extra))
 
     if combined_filename:
         with open(combined_filename, 'wb') as combined:
diff --git a/tests/test_builder.py b/tests/test_builder.py
index b61c651..59b5385 100644
--- a/tests/test_builder.py
+++ b/tests/test_builder.py
@@ -121,8 +121,8 @@ 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 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
+    # size of the file should be 2x the binary version, and the binary is 2 MB
+    assert len(content) == 2 * 2 * 1024 * 1024
 
 
 def test_concatenate_to_uf2_board_only(tmp_path, firmware_binary, config_binary):
@@ -134,8 +134,8 @@ 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 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
+    # 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)
 
 
 def test_padding_firmware(firmware_binary):