diff --git a/smpmgr/main.py b/smpmgr/main.py
index 6ed0cc1..dc41a56 100644
--- a/smpmgr/main.py
+++ b/smpmgr/main.py
@@ -14,7 +14,7 @@
 from smp.os_management import OS_MGMT_RET_RC
 from smpclient.generics import error, error_v1, error_v2, success
 from smpclient.mcuboot import IMAGE_TLV, ImageInfo, TLVNotFound
-from smpclient.requests.image_management import ImageStatesWrite
+from smpclient.requests.image_management import ImageStatesRead, ImageStatesWrite
 from smpclient.requests.os_management import ResetWrite
 from typing_extensions import Annotated, assert_never
 
@@ -169,37 +169,83 @@ def upgrade(
             "(or some other mechanism).",
         ),
     ] = False,
+    bypass_inspect: Annotated[
+        bool,
+        typer.Option(
+            "--bypass-inspect",
+            help="Skip local MCUboot image inspection and read the image hash from the device "
+            "instead of extracting it from the file. "
+            "This is useful when uploading images that are not in MCUboot format, such as "
+            "custom bootloader formats (e.g., NXP's SB3.1) where the hash may be calculated "
+            "differently (e.g., over a specific block rather than the entire binary). "
+            "[bold red]WARNING[/bold red]: When using this option, the responsibility for "
+            "validating image integrity is placed entirely on the device's bootloader. "
+            "If the bootloader does not verify the image, corrupted firmware could be uploaded "
+            "and marked as valid. "
+            "It's assumed the image format encodes some sort of integrity check "
+            "(e.g., CRC or hash)."
+            "[bold red]Only use this option if your bootloader performs its own image integrity "
+            "validation.[/bold red]",
+        ),
+    ] = False,
 ) -> None:
     """Upload a FW image, mark it for next boot, and reset the device."""
 
-    try:
-        image_info = ImageInfo.load_file(str(file))
-        logger.info(str(image_info))
-    except Exception as e:
-        typer.echo(f"Inspection of FW image failed: {e}")
-        raise typer.Exit(code=1)
+    if not bypass_inspect:
+        try:
+            image_info = ImageInfo.load_file(str(file))
+            logger.info(str(image_info))
+        except Exception as e:
+            typer.echo(f"Inspection of FW image failed: {e}")
+            raise typer.Exit(code=1)
 
-    try:
-        image_tlv_sha256 = image_info.get_tlv(IMAGE_TLV.SHA256)
-        logger.info(f"IMAGE_TLV_SHA256: {image_tlv_sha256}")
-    except TLVNotFound:
-        typer.echo("Could not find IMAGE_TLV_SHA256 in image.")
-        raise typer.Exit(code=1)
+        try:
+            image_tlv_sha256 = image_info.get_tlv(IMAGE_TLV.SHA256)
+            logger.info(f"IMAGE_TLV_SHA256: {image_tlv_sha256}")
+        except TLVNotFound:
+            typer.echo("Could not find IMAGE_TLV_SHA256 in image.")
+            raise typer.Exit(code=1)
 
     options = cast(Options, ctx.obj)
     smpclient = get_smpclient(options)
 
     async def f() -> None:
+        image_hash: bytes | None = None
         await connect_with_spinner(smpclient, options.timeout)
 
         with open(file, "rb") as f:
             await upload_with_progress_bar(smpclient, f, slot)
 
         if slot != 0 or confirm:
+            if bypass_inspect:
+                # Read hash from device since we skipped local image inspection
+                r = await smp_request(
+                    smpclient, options, ImageStatesRead(), "Waiting for image states..."
+                )
+
+                if error(r):
+                    print(r)
+                    raise typer.Exit(code=1)
+                elif success(r):
+                    if len(r.images) == 0:
+                        print("No images on device!")
+                        raise typer.Exit(code=1)
+                    for image in r.images:
+                        if image.slot == slot:
+                            image_hash = image.hash
+                            break
+                    if image_hash is None:
+                        print(f"Image with slot {slot} not found!")
+                        raise typer.Exit(code=1)
+                else:
+                    assert_never(r)
+            else:
+                image_hash = image_tlv_sha256.value
+
             image_states_response = await smp_request(
                 smpclient,
                 options,
-                ImageStatesWrite(hash=image_tlv_sha256.value, confirm=confirm),
+                ImageStatesWrite(hash=image_hash, confirm=confirm),
                 "Marking uploaded image for permanent upgrade..."
                 if confirm
                 else "Marking uploaded image for test upgrade...",