diff --git a/core/src/main/java/org/bitcoinj/core/Transaction.java b/core/src/main/java/org/bitcoinj/core/Transaction.java
index 7a6e5234..541ff2b1 100644
--- a/core/src/main/java/org/bitcoinj/core/Transaction.java
+++ b/core/src/main/java/org/bitcoinj/core/Transaction.java
@@ -1755,6 +1755,7 @@ public class Transaction extends ChildMessage {
     /**
      * Returns the transaction {@link #memo}.
      */
+    @Nullable
     public String getMemo() {
         return memo;
     }