diff --git a/core/src/main/java/com/google/bitcoin/core/Wallet.java b/core/src/main/java/com/google/bitcoin/core/Wallet.java
index abc20479..377dbe7f 100644
--- a/core/src/main/java/com/google/bitcoin/core/Wallet.java
+++ b/core/src/main/java/com/google/bitcoin/core/Wallet.java
@@ -455,7 +455,7 @@ public class Wallet implements Serializable, BlockChainListener, PeerFilterProvi
      * @param eventListener callback to be informed when the auto-save thread does things, or null
      */
     public WalletFiles autosaveToFile(File f, long delayTime, TimeUnit timeUnit,
-                                      WalletFiles.Listener eventListener) {
+                                      @Nullable WalletFiles.Listener eventListener) {
         lock.lock();
         try {
             checkState(vFileManager == null, "Already auto saving this wallet.");