diff --git a/src/cmd_pgpcardmake.rs b/src/cmd_pgpcardmake.rs
index 2325f97..11d51d9 100644
--- a/src/cmd_pgpcardmake.rs
+++ b/src/cmd_pgpcardmake.rs
@@ -293,6 +293,8 @@ fn parse_security_sub_key_to_pgp_rsa_private_key(key: &Key<SecretParts, Subordin
         } else {
             return simple_error!("Not unencrypted private key");
         }
+    } else {
+        return simple_error!("Not Key::V4 private key");
     };
     let p = BigNum::from_slice(p.value()).unwrap();
     let q = BigNum::from_slice(q.value()).unwrap();