diff --git a/RSA-encryption.md b/RSA-encryption.md
index 9aac792..60363bd 100644
--- a/RSA-encryption.md
+++ b/RSA-encryption.md
@@ -96,7 +96,8 @@ You can run these commands to generate the private and public key pair:
 openssl genrsa -aes256 -out private.pem 2048
 openssl rsa -in private.pem  -pubout -out public.pem
 ```
-The key needs to be in the PEM format.
+
+The key needs to be in the PKCS#1 format.  If the first line of the private key file is `-----BEGIN PRIVATE KEY-----` rather than `-----BEGIN RSA PRIVATE KEY-----`, then it is in the PKCS#8 format and you'll need to supply the `-traditional` option to openssl.
 
 ### How it works