diff --git a/core/src/main/java/org/bitcoinj/crypto/PBKDF2SHA512.java b/core/src/main/java/org/bitcoinj/crypto/PBKDF2SHA512.java
index 32437f652..94671e117 100644
--- a/core/src/main/java/org/bitcoinj/crypto/PBKDF2SHA512.java
+++ b/core/src/main/java/org/bitcoinj/crypto/PBKDF2SHA512.java
@@ -41,7 +41,7 @@ public class PBKDF2SHA512 {
         ByteArrayOutputStream baos = new ByteArrayOutputStream();
 
         try {
-            int hLen = 20;
+            int hLen = 64;          // Length of HMAC result
 
             if (dkLen > ((Math.pow(2, 32)) - 1) * hLen) {
                 throw new IllegalArgumentException("derived key too long");