diff --git a/firmware/tools/make_image_chunk.py b/firmware/tools/make_image_chunk.py
index 6f75201a..9ecf2c6d 100755
--- a/firmware/tools/make_image_chunk.py
+++ b/firmware/tools/make_image_chunk.py
@@ -56,13 +56,15 @@ if len(sys.argv) == 4:
 		for i in range(4 - (len(input_image) & 3)):
 			input_image.append(0)
 
-	output_image += struct.pack('<4BI', tag[0], tag[1], tag[2], tag[3], len(input_image) - 4)
+	input_image += struct.pack('<4BI', tag[0], tag[1], tag[2], tag[3], len(input_image) - 4)
+	write_image(input_image, output_path)
 
 elif len(sys.argv) == 2:
 	input_image = bytearray()
 	tag = (0, 0, 0, 0)
 	output_path = sys.argv[1]
-	output_image += struct.pack('<4BI', tag[0], tag[1], tag[2], tag[3], 0)
+	input_image += struct.pack('<4BI', tag[0], tag[1], tag[2], tag[3], 0)
+	write_image(input_image, output_path)
 
 else:
 	print(usage_message)
@@ -71,7 +73,3 @@ else:
 if len(tag) != 4:
 	print(usage_message)
 	sys.exit(-2)
-
-output_image = bytearray()
-output_image += input_image
-write_image(output_image, output_path)