diff --git a/ltchiptool/soc/ambz2/util/models/images.py b/ltchiptool/soc/ambz2/util/models/images.py
index 9bfa764..031b752 100644
--- a/ltchiptool/soc/ambz2/util/models/images.py
+++ b/ltchiptool/soc/ambz2/util/models/images.py
@@ -29,6 +29,7 @@
 
 FLASH_CALIBRATION = b"\x99\x99\x96\x96\x3F\xCC\x66\xFC\xC0\x33\xCC\x03\xE5\xDC\x31\x62"
 
+IMAGE_SIGNATURE_OFFSET = 0
 IMAGE_PUBLIC_KEY_OFFSET = 32
 
 
diff --git a/ltchiptool/soc/ambz2/util/ota.py b/ltchiptool/soc/ambz2/util/ota.py
index 12ed7a4..fdff561 100644
--- a/ltchiptool/soc/ambz2/util/ota.py
+++ b/ltchiptool/soc/ambz2/util/ota.py
@@ -1,10 +1,10 @@
 #  Copyright (c) Martin Prokopič 2024-12-02
 
-from .models.images import IMAGE_PUBLIC_KEY_OFFSET
+from .models.images import IMAGE_PUBLIC_KEY_OFFSET, IMAGE_SIGNATURE_OFFSET
 
 
 def patch_firmware_for_ota(data: bytes) -> bytes:
     copy = bytearray(data)
-    copy[0] ^= 0xff  # negate first signature byte
-    copy[IMAGE_PUBLIC_KEY_OFFSET] ^= 0xff  # negate first pubkey byte
+    copy[IMAGE_SIGNATURE_OFFSET] ^= 0xFF  # negate first signature byte
+    copy[IMAGE_PUBLIC_KEY_OFFSET] ^= 0xFF  # negate first pubkey byte
     return bytes(copy)