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