diff --git a/src/main/java/net/schmizz/sshj/common/ECDSAVariationsAdapter.java b/src/main/java/net/schmizz/sshj/common/ECDSAVariationsAdapter.java
index b83a6550..bf810fc7 100644
--- a/src/main/java/net/schmizz/sshj/common/ECDSAVariationsAdapter.java
+++ b/src/main/java/net/schmizz/sshj/common/ECDSAVariationsAdapter.java
@@ -96,7 +96,7 @@ public class ECDSAVariationsAdapter {
         final ECPublicKey ecdsa = (ECPublicKey) pk;
         byte[] encoded = SecgUtils.getEncoded(ecdsa.getW(), ecdsa.getParams().getCurve());
 
-        buf.putString(Integer.toString(fieldSizeFromKey(ecdsa)))
+        buf.putString("nistp" + Integer.toString(fieldSizeFromKey(ecdsa)))
             .putBytes(encoded);
     }