diff --git a/scripts/imgtool.py b/scripts/imgtool.py
index 4f5e56b..8a3e233 100755
--- a/scripts/imgtool.py
+++ b/scripts/imgtool.py
@@ -30,7 +30,8 @@
 
 def do_sign(args):
     align = args.align
-    # print('sign:', args)
+    if args.rsa_pkcs1_15:
+        keys.sign_rsa_pss = False
     img = image.Image.load(args.infile, version=args.version,
             header_size=args.header_size,
             pad=args.pad)
@@ -80,6 +81,8 @@
     sign.add_argument("-H", "--header-size", type=intparse, required=True)
     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',
+            default=False, action='store_true')
     sign.add_argument("infile")
     sign.add_argument("outfile")
 
diff --git a/scripts/imgtool/image.py b/scripts/imgtool/image.py
index 10b2d25..c4bedfe 100644
--- a/scripts/imgtool/image.py
+++ b/scripts/imgtool/image.py
@@ -16,7 +16,8 @@
         'PKCS15_RSA2048_SHA256': 0x0000004,
         'ECDSA224_SHA256':       0x0000008,
         'NON_BOOTABLE':          0x0000010,
-        'ECDSA256_SHA256':       0x0000020, }
+        'ECDSA256_SHA256':       0x0000020,
+        'PKCS1_PSS_RSA2048_SHA256': 0x0000040, }
 
 TLV_VALUES = {
         'SHA256': 1,
diff --git a/scripts/imgtool/keys.py b/scripts/imgtool/keys.py
index d529b59..fc90f9e 100644
--- a/scripts/imgtool/keys.py
+++ b/scripts/imgtool/keys.py
@@ -4,11 +4,16 @@
 
 from Crypto.Hash import SHA256
 from Crypto.PublicKey import RSA
-from Crypto.Signature import PKCS1_v1_5
+from Crypto.Signature import PKCS1_v1_5, PKCS1_PSS
 from ecdsa import SigningKey, NIST256p, util
+import hashlib
 from pyasn1.type import namedtype, univ
 from pyasn1.codec.der.encoder import encode
 
+# By default, we use RSA-PSS (PKCS 2.1).  That can be overridden on
+# the command line to support the older (less secure) PKCS1.5
+sign_rsa_pss = True
+
 AUTOGEN_MESSAGE = "/* Autogenerated by imgtool.py, do not edit. */"
 
 class RSAPublicKey(univ.Sequence):
@@ -47,7 +52,10 @@
 
     def sig_type(self):
         """Return the type of this signature (as a string)"""
-        return "PKCS15_RSA2048_SHA256"
+        if sign_rsa_pss:
+            return "PKCS1_PSS_RSA2048_SHA256"
+        else:
+            return "PKCS15_RSA2048_SHA256"
 
     def sig_len(self):
         return 256
@@ -57,7 +65,10 @@
 
     def sign(self, payload):
         sha = SHA256.new(payload)
-        signer = PKCS1_v1_5.new(self.key)
+        if sign_rsa_pss:
+            signer = PKCS1_PSS.new(self.key)
+        else:
+            signer = PKCS1_v1_5.new(self.key)
         signature = signer.sign(sha)
         assert len(signature) == self.sig_len()
         return signature