diff --git a/doc/imgtool.md b/doc/imgtool.md
index f881d578..309364e0 100644
--- a/doc/imgtool.md
+++ b/doc/imgtool.md
@@ -66,6 +66,7 @@ header and trailer that the bootloader is expecting:
       --align ALIGN
       -v VERSION, --version VERSION
       -H HEADER_SIZE, --header-size HEADER_SIZE
+      --included-header     Image has gap for header
       --pad PAD             Pad image to this many bytes, adding trailer magic
       --rsa-pkcs1-15        Use old PKCS#1 v1.5 signature algorithm
 
@@ -75,8 +76,10 @@ flash device in question, and the header size.
 
 The header size depends on the operating system and the particular
 flash device.  For Zephyr, it will be configured as part of the build,
-and will be a small power of two.  The generated image should start
-with zero bytes of this length (and the script will check this).
+and will be a small power of two.  By default, the header will be
+prepended to the image.  If `--included-header` is given, the image
+must start with header-size bytes of zeros, and the header will be
+overwritten over these bytes.
 
 The optional --pad argument will place a trailer on the image that
 indicates that the image should be considered an upgrade.  Writing
diff --git a/scripts/imgtool.py b/scripts/imgtool.py
index fb09f969..70fdc976 100755
--- a/scripts/imgtool.py
+++ b/scripts/imgtool.py
@@ -34,6 +34,7 @@ def do_sign(args):
         keys.sign_rsa_pss = False
     img = image.Image.load(args.infile, version=args.version,
             header_size=args.header_size,
+            included_header=args.included_header,
             pad=args.pad)
     key = keys.load(args.key)
     img.sign(key)
@@ -79,6 +80,8 @@ def args():
     sign.add_argument("--align", type=alignment_value, required=True)
     sign.add_argument("-v", "--version", type=version.decode_version, required=True)
     sign.add_argument("-H", "--header-size", type=intparse, required=True)
+    sign.add_argument("--included-header", default=False, action='store_true',
+            help='Image has gap for header')
     sign.add_argument("--pad", type=intparse,
             help='Pad image to this many bytes, adding trailer magic')
     sign.add_argument("--rsa-pkcs1-15", help='Use old PKCS#1 v1.5 signature algorithm',
diff --git a/scripts/imgtool/image.py b/scripts/imgtool/image.py
index c4bedfe9..b6a572d2 100644
--- a/scripts/imgtool/image.py
+++ b/scripts/imgtool/image.py
@@ -55,12 +55,17 @@ class TLV():
 
 class Image():
     @classmethod
-    def load(cls, path, **kwargs):
+    def load(cls, path, included_header=False, **kwargs):
         """Load an image from a given file"""
         with open(path, 'rb') as f:
             payload = f.read()
         obj = cls(**kwargs)
         obj.payload = payload
+
+        # Add the image header if needed.
+        if not included_header and obj.header_size > 0:
+            obj.payload = (b'\000' * obj.header_size) + obj.payload
+
         obj.check()
         return obj